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1
W-173  Opportunity Cost and Tradeoffs
Understanding the economic way of thinking reveals the importance of two fundamental concepts: opportunity cost and tradeoffs. Opportunity cost is the value of the next best alternative that is forgon...
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2
W-195  Demand Curves in Economics
Supply and demand are foundational concepts in economics, often illustrated by a graph with the demand curve showing how much of a good people will want at different prices. The demand curve typically...
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3
W-217  Supply Curve in Economics
The supply curve in economics illustrates how much of a product suppliers are willing to offer at different prices. Similar to the demand curve, the supply curve applies to every good and service. Typ...
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4
W-175  How Buyers and Sellers Determine Prices
In economics, the equilibrium price is where the quantity demanded equals the quantity supplied. This price is stable because any deviation from it leads to forces that push the price back towards equ...
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5
W-280  What is GDP?
Gross Domestic Product (GDP) is the total market value of all finished goods and services produced within a country in a year. Imagine the economy as a huge supermarket filled with various products li...
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6
W-224  The Role of Real GDP and Living Standards
Is the economy growing, and are people better off today than in the past? GDP (Gross Domestic Product) helps answer these questions, but it requires adjustments for accuracy. GDP can increase in two w...
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7
W-177  Understanding Real Interest Rates
The nominal interest rate is the rate you typically see on bank or credit card statements and is what most people refer to when they mention "interest rate." However, the real interest rate takes infl...
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8
W-190  The Lifecycle Theory of Savings
The lifecycle theory of savings explains how people choose to spend and save money throughout their lives. This theory considers the typical income pattern that most individuals experience, where inco...
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9
W-201  Natural Rate of Unemployment
The natural rate of unemployment is the unemployment level that would exist in an economy without cyclical unemployment, which is unemployment linked to the business cycle. This natural rate includes ...
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10
W-208  Efficient-Market Hypothesis
The Efficient-Market Hypothesis (EMH) suggests that the prices of assets, like stocks, already include all publicly available information. This means that if you're making investment decisions based o...
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11
W-233  Understanding Real Shocks
Real shocks are unexpected events that can significantly impact an economy by affecting the fundamental factors of production. Examples include droughts, changes in the oil supply, hurricanes, wars, a...
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12
W-251  Understanding Financial Intermediaries
Financial intermediaries are institutions that facilitate the movement of funds between savers and borrowers, making it easier and more efficient for money to flow where it's needed. The most common e...
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13
W-171  Leverage Ratios and Their Risks
A leverage ratio measures the amount of debt a person or company uses compared to their equity, essentially showing how much risk is involved. The concept is illustrated using a housing example. If yo...
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14
W-160  Stagflation: Causes and Challenges
Stagflation is an economic condition where high inflation occurs alongside high unemployment and stagnant demand for products. This situation is unusual because inflation is typically associated with ...
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15
W-199  Understanding Crowding Out in Economic Policy
Crowding out refers to a situation where government spending, especially during full employment, reduces or "crowds out" private spending and investment. When an economy is at full employment, resourc...
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16
W-172  Free Rider Problem and Its Impact on Public Goods
The free rider problem occurs when someone benefits from a good or service without paying for it, leading to potential issues in funding those goods or services. A common example is a group assignment...
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17
W-186  Fisher Effect: Inflation and Interest Rates
The Fisher effect describes the relationship between the inflation rate and the nominal interest rate. It highlights that when inflation is expected to rise, nominal interest rates also increase to ma...
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18
W-223  Opportunity Cost: Making Better Economic Decisions
Opportunity cost refers to the value of the next best alternative that you give up when you choose one option over another. For example, if you decide to wait in line for free ice cream, you're giving...
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19
W-210  Understanding Omitted Variable Bias
Omitted variable bias is a type of selection bias that occurs in regression analysis when important variables are left out, leading to misleading results. This bias happens when a key factor that infl...
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20
W-164  Managing Common Resources
A common resource is a type of good or service that is nonexcludable and rival. "Nonexcludable" means that it is difficult or impossible to prevent people from using the resource, while "rival" means ...
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21
W-164  The Impact of Geography on Economic Growth
Geography plays a crucial role in economic growth, as many of the world's most prosperous cities are located near major bodies of water, such as coasts or rivers. These locations allow for cheaper and...
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22
W-165  How the Stock Market Works
The stock market began in the 1600s when the Dutch East India Company sold shares to private citizens. This helped fund its expensive voyages and created the first stock market. Today, companies use t...
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23
W-177  Why Competing Businesses Cluster Together
Why do similar businesses, like gas stations or coffee shops, often cluster together instead of spreading out? This phenomenon can be explained by Hotelling's Model of Spatial Competition, which illus...
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24
W-160  What Is Dust Made Of?
Dust is made of many tiny things. In houses, it has skin cells, hairs, pet dander, and threads from clothes. Dust mites live in dust and eat dead skin and fungi. Each home’s dust is unique because i...
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25
W-135  Where Do We Get Fresh Water?
Our bodies are mostly water, and fresh water is essential for life. However, only 2.5% of Earth’s water is fresh, and even less is easily usable. Fresh water includes surface water, ice caps, and gr...
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26
W-152  Photosynthesis and Food
Most of the food we eat, like fruits and pasta, contains carbohydrates made of carbon, hydrogen, and oxygen. These atoms come from air, water, and sunlight through photosynthesis in plants. Plants ...
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27
W-145  Why Do Fingers Wrinkle in Water?
When fingers get wet, they wrinkle, a phenomenon scientists have studied for decades. In the 1930s, doctors noticed that people with hand nerve damage did not get wrinkly fingers, suggesting that wrin...
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28
W-176  Why Do Seasons Change?
Seasons change because of Earth's tilt, not its distance from the sun. Earth's orbit is almost circular, so the distance from the sun changes only slightly. In fact, Earth is closer to the sun in Janu...
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29
W-179  What’s Below the Tip of the Iceberg?
Icebergs are mostly underwater because ice is less dense than seawater. About 1/9 of an iceberg is above the surface, and the rest remains hidden. Icebergs form when glaciers, made of compressed fresh...
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30
W-145  The Perilous Journey of Migrating Birds
Each spring, many songbirds return from Central and South America. They travel up to 7,000 miles to breed. Before leaving, birds eat a lot to store energy. While flying, they lose weight quickly. T...
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31
W-172  The life of Penguins.
Penguins are loved worldwide for their charm but face many dangers. Unlike flying birds, they have evolved to swim fast and dive deep with their flipper-like wings and solid bones. Penguins live in th...
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32
W-141  Coelacanth: The Living Fossil
The coelacanth, a fish thought to have gone extinct 65 million years ago, was rediscovered in 1938 near South Africa. This "living fossil" has barely changed in 300 million years. Later, a second spec...
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33
W-128  Why Elephants Never Forget
The saying “elephants never forget” is scientifically accurate. Elephants can recognize up to 30 herd members and remember other animals and humans for decades. Their large brain, comparable to a ...
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34
W-144  How Do We Breathe?
Breathing keeps us alive by delivering oxygen to our bodies. Air enters through the nose or mouth and moves to the lungs' alveoli, where oxygen is absorbed into the blood. The diaphragm and intercosta...
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35
W-135  Why Mosquitoes Bite Some People More
Mosquitoes prefer some people over others due to several factors. Female mosquitoes feed on blood to support egg production and use specialized sensors to detect their preferred hosts. They are attrac...
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36
W-145  How Did Museums Begin?
Museums have a history of over 2,000 years, evolving greatly from their origins. The word "museum" comes from the Greek "mouseion," temples for the Muses, where offerings like sculptures and scientifi...
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37
W-162  A Brief History of Plastic
Plastics originated from the need to replace materials like ivory in the 19th century. In 1863, John Wesley Hyatt invented celluloid, the first plastic, made from cellulose. Although celluloid was fla...
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38
W-146  Why Can’t You Put Metal in a Microwave?
Microwave ovens use electromagnetic waves to heat food by making polar molecules, like water, vibrate and create frictional heat. This technology, originally developed for RADAR in World War II, doesn...
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39
W-128  What Happens If You Don’t Put Your Phone in Airplane Mode?
Phones emit strong radio wave signals to connect with cell towers. In flight, phones work harder to find service due to the distance from towers, broadcasting loud signals that can overwhelm ground co...
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40
W-141  Were Long Necks Also Tall Necks?
Sauropod dinosaurs, known for their incredibly long necks, raise questions about how these necks were positioned—vertically, horizontally, or somewhere in between. Paleontologists debate this be...
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41
W-145  Did Dinosaurs Really Have Feathers?
Scientists have confirmed that many dinosaurs, especially theropods like Velociraptors and possibly T. Rex, had feathers. Fossils discovered over the past 20 years, especially in China, show clear evi...
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42
W-149  Why Do Cats Purr?
Cats purr by using their larynx and diaphragm muscles, creating rhythmic vibrations between 25 and 150 hertz during inhaling and exhaling. While purring is often associated with happiness, cats also p...
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43
W-176  Why Mammals Are Smaller Than Dinosaurs
Long ago, dinosaurs grew very big. One dinosaur, Amphicoelias Fragillimus, was 60 meters long and weighed 122 tons. Today, the biggest land mammal is the African elephant. It is only 5.5 tons and 3-4 ...
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44
W-141  Bananas: Not What They Seem
Bananas are popular and nutritious fruits that people love for their convenience. However, bananas today are not like wild bananas. Wild bananas have seeds, but the bananas we eat, like the Cavendish,...
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45
W-170  Why Sleep Is Essential
Sleep is something everyone needs, but scientists still do not fully understand why. Sleep helps our brains and bodies rest and recover. It may also help us survive by keeping us safe and saving energ...
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46
W-181  What Happens When You Stop Eating
Starvation happens when the body doesn’t get enough food. Without oxygen, people die in minutes. Without water, they last a few days. But without food, a person can survive for weeks or even two mon...
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47
W-141  How Oysters Make Pearls
Pearls are not mined from the earth but made inside oysters. This happens when something small, like a bit of food, gets trapped between the oyster’s soft tissue and hard shell. This irritates the o...
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48
W-187  Do We Only Use 10% of Our Brain?
People often say humans use only 10% of their brains. This idea is popular in movies and speeches, but it is not true. Scientists have proven that we use every part of our brain. Brain scans like M...
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49
W-145  Why Do We Need to Save Money?
Saving money means keeping some money for later. People do not spend all their money at once. They put some in a bank or a piggy bank. This is called saving. Why do people save money? Sometimes, th...
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50
W-149  What Is a Bank?
A bank is a place where people keep their money safe. People put money into the bank. This is called a deposit. They can also take money out. That is called a withdrawal. Banks help people save mon...
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51
W-142  How Should We Use Our Allowance?
An allowance is money children get from parents. They might get it every week or month. Some kids get allowance for doing chores like cleaning or helping at home. It is important to use allowance w...
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52
W-200  How Is the Price Decided?
When you go to a store, you see price tags on things. A toy may cost ten dollars, and a book may cost five. But who decides these prices? And why do some things cost more than others? First, prices...
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53
W-161  Why Do We Get Money for Work?
People work every day. Some people cook food, some teach students, and some build houses. But why do they get money for their work? When someone works, they help others. A cook makes food for peopl...
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54
W-166  Why Are Toys Expensive?
Have you ever wanted a toy but saw that it cost a lot of money? Some toys are very expensive. But why are they so costly? First, toys are made in factories. People use machines and materials like p...
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55
W-144  What Should We Think About When Buying Things?
When we go shopping, we see many things we want to buy. But before we buy something, it is smart to think first. What should we think about? First, ask yourself, “Do I really need this?” Someti...
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56
W-231  Where Do We Keep Money?
Money is something we use every day. We use money to buy things like food, toys, and clothes. Because money is important, we must keep it safe. But where can we keep our money? Some people keep the...
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57
W-150  Why Do We See Advertisements?
We see ads on TV, on the internet, and on the street. But why are there so many ads? Ads tell us about things we can buy. We can see ads for toys, food, or clothes. If something is new, an ad shows...
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58
W-167  Why Do People Run a Business?
Some people open a store. Some sell food, some sell clothes, and some sell toys. This is called doing business. But why do people do business? People do business to make money. When they sell thing...
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59
W-189  How Does a Store Owner Make Money?
A store owner is a person who has a shop. The shop may sell food, toys, or clothes. But how does the store owner make money? First, the owner buys things from a factory or big store. Then, they sel...
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60
W-180  Why Do Stores Have Sales?
Sometimes we see signs that say “SALE” in front of stores. The prices are lower than usual. But why do stores have sales? Stores have sales to get more people to buy things. When the price is l...
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61
W-171  Why Is Giving a Good Thing?
Sometimes, people give money, food, or clothes to others. This is called giving or donating. But why is giving a good thing? Some people do not have enough. They may not have food to eat or warm cl...
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62
W-174  How Does Online Shopping Work?
Many people shop on the internet. This is called online shopping. But how does it work? First, you go to a website or app. There, you can see pictures of things like toys, clothes, or food. You cli...
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63
W-168  Where Do Things Come From?
Every day, we use many things. We wear clothes, eat food, and play with toys. But where do these things come from? Many things come from factories. A factory is a big building where people and mach...
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64
W-163  How Did Bartering Work?
A long time ago, people did not use money. They used bartering. Bartering means trading things. People gave one thing and got another thing they needed. For example, one person had apples. Another ...
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65
W-172  What Is the Economy?
We hear the word “economy” on TV or at school. But what does it mean? The economy is how people make, use, and share things like food, clothes, and money. It is about how people work and trade....
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66
W-148  Needs and Wants: What’s the Difference?
We use money to buy many things. But some things are needs, and some are wants. What is the difference? Needs are things we must have to live. We need food, water, clothes, and a home. These help u...
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67
W-164  Why Should We Save Money?
Sometimes we get money from our parents or as a gift. We may want to spend it right away. But saving money is also important. Why should we save money? Saving money means keeping it to use later. W...
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68
W-158  How Did People Live Without Money?
A long time ago, there was no money. But people still needed food, clothes, and tools. So how did they live? People used bartering. This means they traded things. One person gave something and got ...
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69
W-161  What Is a Job?
A job is work that people do to make money. Many adults have jobs. They use the money to buy food, clothes, and pay for their home. There are many kinds of jobs. A teacher helps children learn. A d...
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70
W-155  What Can We Buy at the Market?
A market is a place where people buy and sell things. Many people go to the market to get what they need. But what can we buy at the market? We can buy food. There are fruits like apples, bananas, ...
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71
W-156  Why Is Money Different in Each Country?
People all over the world use money. But not all money looks the same. Why is money different in each country? Each country has its own money. In the USA, people use dollars. In Korea, people use w...
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72
W-204  Why Are Price Tags Necessary?
Price tags are very important in stores and markets. They show how much something costs. Without price tags, people wouldn’t know how much money they need to pay for an item. When you go to a sto...
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73
W-178  How Is Money Made?
Money is something we use every day. We use it to buy food, toys, and clothes. But have you ever thought about how money is made? Each country makes its own money. In Korea, the government makes mo...
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74
W-160  What Is the Difference Between Expensive and Cheap?
When we go shopping, we see things with different prices. Some things cost a lot. Some cost a little. These are called expensive and cheap. But what is the difference? Expensive things cost more mo...
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75
W-147  How Are Taxes Used?
Taxes are money that people pay to the government. But why do we pay taxes, and how are they used? People pay taxes when they buy things or earn money. This money goes to the government. The govern...
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W-165  What Kind of Money Will We Use in the Future?
Today, we use coins, bills, and cards to buy things. But what kind of money will we use in the future? In the future, we may use less paper money. Many people already use phones or computers to pay...
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