Money · applications

Applications: Money

10 question types · Primary 2 · each worked step by step with a figure that follows the steps

PSLE

01

A Handful of Mixed Coins Counted

strategyBiggest Coin First / Count On One Coin at a Time

Mei has four coins in her hand: a 20-cent coin, a 5-cent coin, a 50-cent coin and another 20-cent coin. (a) How much money does Mei have? (b) Mei finds one more 5-cent coin. How much money does she have now?

50¢20¢20¢5¢
The four coins, with the biggest value first.
Put the coins in order, biggest first: 50 cents, 20 cents, 20 cents, 5 cents.
step 1 of 4

Put the coins in order from the biggest value to the smallest. Then count on, one coin at a time, and say the new total after each coin.

  1. Put the coins in order, biggest first: 50 cents, 20 cents, 20 cents, 5 cents.
  2. Start with the biggest coin and count on: 50, then 50 + 20 = 70, then 70 + 20 = 90.
  3. (a) Add the last coin: 90 + 5 = 95. Mei has 95 cents.
  4. (b) One more 5-cent coin makes 95 + 5 = 100 cents. 100 cents is $1.

answer(a) 95 cents; (b) 100 cents, which is $1

techniqueCounting Coins

examsPSLE

Common pitfalls

  • Counting the coins and saying that Mei has 4 cents. Four is the number of coins. Each coin is worth its own amount, so the amounts are added.
  • Starting with the small coins: 5 + 20 + 50 + 20. The total is the same, but the adding is harder. Starting with the biggest coin gives easy steps: 50, 70, 90, 95.
02

The Same Amount Made with the Fewest Coins

strategyTake the Biggest Coin That Fits Each Time

A sticker costs 80 cents. (a) Siti pays with 20-cent coins only. How many coins does she use? (b) Ali pays 80 cents with the fewest coins he can. How many coins does he use?

Siti20¢20¢20¢40¢20¢60¢20¢80¢
Count in twenties up to 80: 20, 40, 60, 80.
Count in twenties up to 80: 20, 40, 60, 80.
step 1 of 5

The same amount can be made in more than one way. Big coins reach the amount in fewer steps, so for the fewest coins take the biggest coin that fits each time.

  1. Count in twenties up to 80: 20, 40, 60, 80.
  2. (a) That is 4 twenties, so Siti uses 4 coins.
  3. For the fewest coins, take the biggest coin that fits. A $1 coin is too much. A 50-cent coin fits, and 80 − 50 = 30 cents are still needed.
  4. A 20-cent coin fits next, and 30 − 20 = 10 cents are still needed. A 10-cent coin finishes it.
  5. (b) Ali uses 3 coins: 50 + 20 + 10 = 80 cents.

answer(a) 4 coins; (b) 3 coins

techniqueCounting Coins

examsPSLE

Common pitfalls

  • Thinking that more coins means more money. Siti uses 4 coins and Ali uses 3 coins, and both pay 80 cents.
  • Taking two 50-cent coins because they are the biggest. 50 + 50 = 100 cents, which is more than 80 cents. Each coin must fit into what is still needed.
03

Enough Money for Two Things or Not

strategyAdd the Dollars, Add the Cents, Then Compare

Ravi has a $5 note. A toy car costs $3.20 and a ball costs $2.50. (a) How much do the toy car and the ball cost altogether? (b) Does Ravi have enough money to buy both? If not, how much more money does he need?

toy car$3.20ball$2.50Ravi has$5$3 + $2 = $5
Add the dollars with the dollars: $3 + $2 = $5.
Add the dollars with the dollars: $3 + $2 = $5.
step 1 of 4

Add the dollars with the dollars and the cents with the cents to find the total cost. Then compare the total cost with the money Ravi has.

  1. Add the dollars with the dollars: $3 + $2 = $5.
  2. Add the cents with the cents: 20 + 50 = 70 cents.
  3. (a) The two things cost $5 and 70 cents, which is $5.70 altogether.
  4. (b) Compare $5.70 with the $5 that Ravi has. The cost is more, so he does not have enough. He needs 70 cents more.

answer(a) $5.70; (b) No. Ravi needs 70 cents more.

techniqueAdding and Subtracting Money · Dollars and Cents

examsPSLE

Common pitfalls

  • Looking only at the dollars. $3 + $2 = $5 looks like enough, but the cents still have to be paid, and they are 20 + 50 = 70 cents more.
  • Comparing the $5 note with each price on its own. $5 is enough for the toy car alone and for the ball alone, but the question asks about both together.
04

Change from a One-Dollar Coin and from a Two-Dollar Note

strategyCount Up to the Next Ten Cents, Then to the Dollar

An eraser costs 75 cents. (a) Lina pays with a $1 coin. How much change does she get? (b) Tom buys the same eraser and pays with a $2 note. How much change does he get?

75¢80¢$1+5¢
From 75 cents to the next ten cents is 5 cents.
Start at the price, 75 cents. Count up to the next ten cents: 75 + 5 = 80.
step 1 of 5

The change is the distance from the price up to the money paid. Count up in easy jumps on a number line, first to the next ten cents and then to the dollar, and add the jumps.

  1. Start at the price, 75 cents. Count up to the next ten cents: 75 + 5 = 80.
  2. Count up from 80 cents to $1, which is 100 cents: 80 + 20 = 100.
  3. (a) Add the jumps: 5 + 20 = 25. Lina gets 25 cents change.
  4. For Tom, count up one more jump, from $1 to $2. That jump is $1.
  5. (b) Tom gets $1 and 25 cents, which is $1.25 change. Check: 75 cents and $1.25 make $2.

answer(a) 25 cents; (b) $1.25

techniqueMaking Change · Counting Coins

examsPSLE

Common pitfalls

  • Giving the price as the change. 75 cents is what the shop keeps. The change is what is left of the $1 after the eraser is paid for.
  • Counting up to $1 and stopping when the money paid was $2. The count has to go all the way to the amount paid.
05

Change from a Note for a Price in Dollars and Cents

strategyCount Up to the Next Dollar, Then to the Note

A toy costs $6.40. (a) Mei pays with a $10 note. How much change does she get? (b) Her brother buys the same toy. He pays with a $5 note and a $2 note. How much change does he get?

paid$10$6.40$7$10+60¢
From $6.40 to the next dollar is 60 cents.
Start at the price, $6.40. Count up to the next dollar: 40 + 60 = 100 cents, so 60 cents more makes $7.
step 1 of 5

Count up from the price to the money paid. The first jump finishes the dollar, and the second jump is in whole dollars.

  1. Start at the price, $6.40. Count up to the next dollar: 40 + 60 = 100 cents, so 60 cents more makes $7.
  2. Count up from $7 to $10: 7 + 3 = 10, so that jump is $3.
  3. (a) Mei gets $3 and 60 cents, which is $3.60 change.
  4. Her brother pays $5 + $2 = $7. Counting up from $6.40 stops at $7, after the first jump.
  5. (b) He gets 60 cents change. Check: $6.40 and 60 cents make $7.

answer(a) $3.60; (b) 60 cents

techniqueMaking Change · Dollars and Cents

examsPSLE

Common pitfalls

  • Taking only the dollars away, $10 − $6 = $4, and then writing $4.40. The 40 cents are part of the price, so the change is less than $4, not more.
  • Writing 60 cents as $0.06. Sixty cents is written $0.60, and $0.06 is only 6 cents.
06

A Jar of Ten-Cent Coins in Dollars and Cents

strategyTen Ten-Cent Coins Make One Dollar / One Hundred Cents Is One Dollar

Ben empties his jar. It has 24 ten-cent coins in it. (a) How much money is in the jar? Give the answer in dollars and cents. (b) Ben wants to have $3. How many more ten-cent coins does he need?

10¢10¢10¢10¢10¢10¢10¢10¢10¢10¢$110¢10¢10¢10¢10¢10¢10¢10¢10¢10¢10¢10¢10¢10¢
A full row is ten 10-cent coins. That is 100 cents, which is $1.
Put the coins in rows of 10. Ten 10-cent coins are 100 cents, and 100 cents is $1.
step 1 of 5

Put the coins in rows of ten. Each full row is 100 cents, which is one dollar, and the coins in the last row are the cents.

  1. Put the coins in rows of 10. Ten 10-cent coins are 100 cents, and 100 cents is $1.
  2. 24 coins make 2 full rows and 4 more coins. That is $2 and 4 × 10 = 40 cents.
  3. (a) There are 240 cents in the jar, which is $2.40.
  4. $3 is 300 cents. Count up from 240 in tens: 250, 260, 270, 280, 290, 300. That is 6 tens.
  5. (b) Ben needs 6 more ten-cent coins. Check: 4 + 6 = 10 coins fill the third row.

answer(a) $2.40; (b) 6 coins

techniqueDollars and Cents · Counting Coins

examsPSLE

Common pitfalls

  • Writing 24 coins as 24 cents. Each coin is worth 10 cents, so the coins are counted in tens, and 24 tens are 240 cents.
  • Writing 240 cents as $240. One dollar is 100 cents, so 240 cents is 2 dollars and 40 cents, which is $2.40.
07

More Coins or More Money

strategyCount the Value, Not the Number of Coins

Lina has 5 coins: three 20-cent coins and two 5-cent coins. Tom has 3 coins: a 50-cent coin and two 20-cent coins. (a) Who has more money? (b) How much more?

Lina: 5 coins20¢20¢20¢40¢20¢60¢5¢65¢5¢70¢Tom: 3 coins50¢20¢20¢
Lina has 20, 40, 60, 65, 70 cents.
Count what Lina has, biggest coin first: 20, 40, 60, then 65, 70. Lina has 70 cents.
step 1 of 4

The number of coins does not tell how much money there is. Count what each child's coins are worth, and then compare the two amounts.

  1. Count what Lina has, biggest coin first: 20, 40, 60, then 65, 70. Lina has 70 cents.
  2. Count what Tom has, biggest coin first: 50, 70, 90. Tom has 90 cents.
  3. (a) 90 cents is more than 70 cents, so Tom has more money, with fewer coins.
  4. (b) Count up from 70 to 90: 70 + 20 = 90. Tom has 20 cents more.

answer(a) Tom. He has 90 cents and Lina has 70 cents; (b) 20 cents more

techniqueCounting Coins

examsPSLE

Common pitfalls

  • Saying that Lina has more because she has 5 coins and Tom has 3. The number of coins does not tell what they are worth. One 50-cent coin is worth more than two 20-cent coins.
  • Counting every coin as the same amount. A 5-cent coin, a 20-cent coin and a 50-cent coin are worth different amounts, so read the value on each coin.
08

The Same Amount Saved Every Day

strategyCount On One Day at a Time / Two Fifty-Cent Coins Make a Dollar

Siti puts a 50-cent coin into her money box every day. (a) How much money does she save in 7 days? (b) She wants to buy a book that costs $4.50. How many days does she need to save for it altogether?

day 150¢50¢day 250¢$1
Two 50-cent coins make $1. Siti saves $1 every 2 days.
Two 50-cent coins make 100 cents, which is $1. So every 2 days Siti saves $1.
step 1 of 5

Draw one coin for each day and write the total under it. Two 50-cent coins make one dollar, so the total is easy to say as it grows.

  1. Two 50-cent coins make 100 cents, which is $1. So every 2 days Siti saves $1.
  2. Count on one day at a time: 50 cents, $1, $1.50, $2, $2.50, $3, $3.50.
  3. (a) In 7 days Siti saves $3.50.
  4. Keep counting until the total reaches $4.50. Day 8 makes $4 and day 9 makes $4.50.
  5. (b) Siti needs 9 days altogether.

answer(a) $3.50; (b) 9 days

techniqueDollars and Cents · Counting Coins

examsPSLE

Common pitfalls

  • Writing 7 × 50 = 350 and giving the answer as $350. The 350 is in cents, and 350 cents is $3.50.
  • Answering 2 days for part (b). Two more days are needed after the first 7, but the question asks for all the days: 7 + 2 = 9.
09

Two Prices Whose Cents Make More Than a Dollar

strategyAdd the Cents / Change One Hundred Cents for One Dollar

A bun costs 85 cents and a packet of milk costs 60 cents. (a) Ali buys one bun and one packet of milk. How much does he pay? (b) Mei buys two buns and one packet of milk. How much does she pay?

Alibun 85¢milk 60¢145¢
Add the cents: 85 + 60 = 145 cents.
Add the cents: 85 + 60 = 145 cents.
step 1 of 5

Add the cents first. When the cents come to 100 or more, change each 100 cents for one dollar and write what is left as the cents.

  1. Add the cents: 85 + 60 = 145 cents.
  2. 145 cents is more than 100 cents. Change 100 cents for $1: 145 = 100 + 45.
  3. (a) Ali pays $1 and 45 cents, which is $1.45.
  4. Mei pays for one more bun: 145 + 85 = 230 cents. Change 200 cents for $2: 230 = 200 + 30.
  5. (b) Mei pays $2.30.

answer(a) $1.45; (b) $2.30

techniqueAdding and Subtracting Money · Dollars and Cents

examsPSLE

Common pitfalls

  • Writing 145 cents as $145. One dollar is 100 cents, so 145 cents is 1 dollar and 45 cents, which is $1.45.
  • Adding only one bun for Mei. She buys two buns, so 85 cents is added twice: 85 + 85 + 60 = 230 cents.
10

Coins Moved So That Two Children Have the Same Amount

strategyMove One Coin at a Time / One Goes Down as the Other Goes Up

Ali has four 20-cent coins. Ben has two 20-cent coins. Ali gives some of his coins to Ben so that both boys have the same amount of money. (a) How much money does each boy have then? (b) How much money does Ali give to Ben?

Ali20¢20¢20¢40¢20¢60¢20¢80¢Ben20¢20¢20¢40¢
Ali has 80 cents and Ben has 40 cents.
Count each boy's money. Ali has 20, 40, 60, 80 cents. Ben has 20, 40 cents.
step 1 of 4

Count what each boy has. Then move one coin at a time from Ali to Ben. Each move makes Ali's amount smaller and Ben's amount bigger, so stop as soon as the two amounts are the same.

  1. Count each boy's money. Ali has 20, 40, 60, 80 cents. Ben has 20, 40 cents.
  2. Move one coin from Ali to Ben. Ali now has 80 − 20 = 60 cents and Ben has 40 + 20 = 60 cents.
  3. (a) The two amounts are the same now. Each boy has 60 cents.
  4. (b) Only one coin was moved, so Ali gives Ben 20 cents. Check: there are 6 coins in all, and each boy has 3 of them.

answer(a) 60 cents each; (b) 20 cents

techniqueCounting Coins · Adding and Subtracting Money

examsPSLE

Common pitfalls

  • Giving Ben the whole difference. Ali has 80 − 40 = 40 cents more, but if he gives away 40 cents he has 40 cents left and Ben has 80 cents. Ali gives only half of the difference.
  • Forgetting that the coin leaves Ali. When a coin is moved, Ali's money goes down and Ben's money goes up at the same time.
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