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Shopping play

Ratio, rates and money · level 1, lesson 5 of 5

A question to start

Welcome to the toy shop! Here is what is on the shelf today.

  • A bouncy ball costs 1 dollar.
  • A toy car costs 2 dollars.
  • A small teddy costs 3 dollars.

You have 4 loonies in your pocket. Can you buy the car and the teddy? Can you buy the ball and the teddy? What is the most toys you could take home?

Shopping is one of the first places where math really matters. If you get it wrong, you either cannot pay, or you give away more money than you need to. In this lesson you will play shop, pay with loonies and toonies, and learn how to tell which toy costs more and what you can afford.

The idea

Price tags

The price of a thing is how much money you must pay for it. Shops show the price on a small card or sticker called a price tag.

1 dollar2 dollars3 dollars

To buy a thing, you give the shopkeeper money worth the price. Then the thing is yours.

Paying with loonies

A loonie is worth 1 dollar (you met it in Canadian coins). So paying with loonies is just counting:

  • The ball costs 1 dollar: give 1 loonie.
  • The car costs 2 dollars: give 2 loonies.
  • The teddy costs 3 dollars: give 3 loonies.

The number of loonies is the same as the number of dollars. That is because there is 1 dollar for every loonie. It is a "for every" rule, just like 2 wheels for every bike.

Which costs more?

To find which toy costs more, compare the prices. The bigger number of dollars costs more.

  • The car (2 dollars) costs more than the ball (1 dollar).
  • The teddy (3 dollars) costs more than the car (2 dollars).
  • So the teddy costs the most, and the ball costs the least.

With loonies, you can see which costs more. Put the loonies for each toy in a tower.

ballcarteddy

The tallest tower costs the most. How much more does the teddy cost than the car? Put the towers side by side: the teddy tower has 1 more loonie. So the teddy costs 1 dollar more.

Paying for two things

When you buy two toys, you pay for both. Put their loonies together.

  • Ball and car: 1 loonie and 2 loonies make 3 loonies.
  • Car and teddy: 2 loonies and 3 loonies make 5 loonies.

Now we can answer the first question. You have 4 loonies. The car and the teddy cost 5 loonies together. 4 is less than 5, so you cannot buy both. You are 1 loonie short.

But the ball and the teddy cost 1 and 3, which make 4 loonies. You have exactly 4. Yes, you can buy those two!

When you have enough money to buy something, we say you can afford it.

A toonie is two loonies

A toonie is worth 2 dollars, the same as 2 loonies. So you can pay with a toonie in place of 2 loonies.

  • The car costs 2 dollars. You can pay with 1 toonie.
  • The teddy costs 3 dollars. You can pay with 1 toonie and 1 loonie (2 dollars and 1 dollar make 3 dollars).

Be careful: a toonie is one coin, but it is worth two dollars. When you count your money, count the dollars, not the coins.

Getting money back

What if you only have a toonie, and you buy the ball for 1 dollar? You give the toonie, which is 2 dollars. That is 1 dollar too much. So the shopkeeper gives you 1 loonie back. Money given back like this is called change. You will learn all about change in level 2.

Worked examples

Example 1. Paying. A kite costs 3 dollars. How many loonies do you give?

  1. There is 1 dollar for every loonie.
  2. 3 dollars needs 3 loonies. Count them out: one, two, three.

Example 2. Which costs more, and by how much? A crayon box costs 2 dollars. A colouring book costs 4 dollars.

  1. Compare the prices: 4 is more than 2. So the colouring book costs more.
  2. How much more? Make towers of loonies: 2 and 4. Count up from 2 to 4: "3, 4". That is 2 more.
  3. The colouring book costs 2 dollars more.

Example 3. Can I afford it? You have 1 toonie and 1 loonie. Can you buy a puzzle that costs 4 dollars?

  1. Count your money in dollars, not coins. A toonie is 2 dollars. A loonie is 1 dollar.
  2. 2 dollars and 1 dollar make 3 dollars.
  3. The puzzle costs 4 dollars. 3 is less than 4.
  4. No, you cannot afford it yet. You need 1 more dollar.

Example 4. Making the most of your money. You have 5 loonies. The shop has a ball (1 dollar), a car (2 dollars) and a teddy (3 dollars). You want as many toys as you can get, and you can buy more than one of the same toy. What is the most toys you can buy?

  1. To get the most toys, buy the cheapest ones. The ball costs the least.
  2. 5 loonies buy 5 balls (1 loonie each). That is 5 toys.
  3. What if you want one of each toy? Ball, car and teddy cost 1, 2 and 3 loonies. Put them together: 1 and 2 make 3, and 3 more make 6. You have only 5 loonies, so one of each is too much, by 1 loonie.
  4. You could take the teddy and a ball (3 and 1 make 4), then one more ball with the last loonie. That is 3 toys and no money left. Or a ball and two cars (1 and 2 and 2 make 5): 3 toys too.

The cheapest toys give you the most things. But you may like the teddy more than 5 balls! Math tells you what you can buy. You decide what you want to buy.

Try it

  1. A sticker costs 1 dollar. A yo-yo costs 3 dollars. Which costs more?
  2. How many loonies do you need to buy a toy that costs 2 dollars?
  3. You buy a ball (1 dollar) and a car (2 dollars). How many loonies do you pay?
  4. You have 3 loonies. Can you buy a teddy that costs 3 dollars? Will you have any money left?
  5. You have 1 toonie. Which of these can you buy: a ball (1 dollar), a car (2 dollars), a teddy (3 dollars)?
  6. A book costs 3 dollars and a puzzle costs 1 dollar. How much more does the book cost?
  7. Ella has 2 coins worth 3 dollars together. Which coins are they?
  8. You have 6 loonies. You want a car (2 dollars) and a teddy (3 dollars). Can you buy both? How many loonies are left?
Answers
  1. The yo-yo. 3 dollars is more than 1 dollar.
  2. 2 loonies. There is 1 dollar for every loonie.
  3. 3 loonies. 1 loonie and 2 loonies make 3.
  4. Yes. 3 loonies is 3 dollars, exactly the price. You will have no money left.
  5. A toonie is 2 dollars. You can buy the ball (and get 1 dollar back as change) or the car (exactly 2 dollars). You cannot buy the teddy, because 3 dollars is more than 2.
  6. 2 dollars more. Count up from 1 to 3: "2, 3". That is 2 steps.
  7. A toonie and a loonie. 2 dollars and 1 dollar make 3 dollars. (Two loonies make only 2 dollars, and two toonies make 4 dollars.)
  8. Yes. The car and teddy cost 2 and 3, which make 5 dollars. You have 6. Take away 5 loonies, and 1 loonie is left.

Common mistake

Counting coins instead of dollars. A toonie is one coin, but it is 2 dollars. "I have 2 coins, so I have 2 dollars" is wrong if one of the coins is a toonie. Say the worth of each coin as you count: "2 dollars, 3 dollars".

Forgetting to put both prices together. To buy two things, you must pay for both. Having enough for each one by itself is not the same as having enough for the two together.

Where it leads