Numbers and operations · Ages 12–13

Estimating when shopping worksheet

Part of: Approximation & estimation

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Numbers and operations · Ages 12–13

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Write each answer in the space. For word problems, show your working and write a sentence answer.

1.$21.5, $9.5, $20.8: with each price rounded up to the dollar, the estimated total is $.
Answer:
2.Buying $8.5, $16.2 and $11.4, paying $50. Rounded up, the total is $, so the change is at least $.
Fill in each blank
Answer:
3.Notebooks cost $1.7 each. At most how many can $100 buy?
Answer:
4.$80.2, $67.6, $68.7: with each price rounded down to the dollar, the estimated total is $.
Answer:
5.Buying $25.4, $11.7 and $26.4, paying $100. Rounded up, the total is $, so the change is at least $.
Fill in each blank
Answer:
6.8 tickets at $94 each. What is the fewest $100 notes to take?
Answer:

7.You have $60 and want three things: $12.4, $23.2 and $8.4. To be sure, by estimating, that the money is enough, what should you do to each price?
- A. Count only the dearest
- B. Round it off to the dollar
- C. Round it down to the dollar
- D. Round it up to the dollar
Choose the right answer
Answer:
8.$16.8, $9.6, $8.8: rounding the prices up to the dollar shows for sure that $35 is enough.
True or false?
Answer:
9.$25.1, $7.1, $22.6: rounding the prices up to the dollar shows for sure that $60 is enough.
True or false?
Answer:
10.Buying $28.7, $21.9 and $29.4 with $75. Which conclusion and reason are both right?
- A. Not enough: rounded down, $78 is already over $75
- B. Enough: rounded down, $78 is within $75
- C. Enough: rounded up, $81 is within $75
- D. Not enough: rounded up, $81 is over $75
Choose the right answer
Answer:
11.$36.6, $59.5, $38.1: rounding the prices down to the dollar shows for sure that the total reaches $131.
True or false?
Answer:
12.$59.5, $51.4, $98.9: rounding the prices down to the dollar shows for sure that the total reaches $207.
True or false?
Answer:

13.Spend $40 for a free bag. Choosing items at $15.8, $13.3 and $16.6, to be sure by estimating that you have spent $40, what should you do to each price?
- A. Round it off to the dollar
- B. Count only the cheapest
- C. Round it down to the dollar
- D. Round it up to the dollar
Choose the right answer
Working:
Answer:
14.An online shop delivers free from $300. With $253 of goods chosen, socks at $27 a pair are added. At least how many pairs?
Working:
Answer:
15.At the supermarket: $74, $47, $45, $17. With each price rounded up to the tens, the estimated total is $; paying $400, the change is at least $.
Fill in each blank
Working:
Answer:
16.A bakery uses between 32 kg and 44 kg of flour a day. Ordering a week's flour so it never runs out, how many kg a day should the order allow?
- A. 44
- B. 76
- C. 32
- D. 38
Choose the right answer
Working:
Answer:
17.May has $69 for three items of stationery at $26.8, $25.6 and $15.5. May has enough for all three.
True or false?
Working:
Answer:
18.5 lunches at $35.7 each. What is the fewest $50 notes to hand over?
Working:
Answer:

Show the answers and working

Estimating when shopping worksheet: Answers and working

1. 53
22 + 10 + 21 = 53. Rounding up: any cents at all make one more dollar.
2. 38, 12
Rounded up, 38 is too big, so no more than that is spent: the change is at least 50 − 38 = 12 dollars.
3. 58 notebooks
100 ÷ 1.7 ≈ 58.82, which is rounded down: at most 58. A notebook you can't afford doesn't count.
4. 215
80 + 67 + 68 = 215. Rounding down: the cents all go.
5. 65, 35
Rounded up, 65 is too big, so no more than that is spent: the change is at least 100 − 65 = 35 dollars.
6. 8 notes
8 × 94 = 752, and 752 ÷ 100 is rounded up: 8. Part of a note's worth still needs a whole note.

7. D. Round it up to the dollar
Rounded up, every price is too big, so the total, 46, is too big; if even that is within 60, the money is surely enough.
8. False
Rounded up, the estimate is 36, which is too big. Only if it is within the budget are you sure; if it isn't, you must work it out exactly.
9. True
Rounded up, the estimate is 57, which is too big. Only if it is within the budget are you sure; if it isn't, you must work it out exactly.
10. A. Not enough: rounded down, $78 is already over $75
To be sure it is enough, use the estimate that is too big (rounded up, 81); to be sure it isn't, the one that is too small (rounded down, 78).
11. True
Rounded down, the estimate is 133, which is too small. Only if even that reaches 131 is the real total sure to.
12. True
Rounded down, the estimate is 208, which is too small. Only if even that reaches 207 is the real total sure to.

Marking: 2 for the working, 1 for the answer, 1 for the sentence.

13. C. Round it down to the dollar
Rounded down, the estimate is too small; if even that reaches $40, the real total surely does.
14. 2 pairs
$47 short: 300 − 253 = 47, and 47 ÷ 27 rounded up is 2 pairs.
15. 200, 200
Rounded up, 200 is too big, so no more is spent: the change is at least 400 − 200 = 200 dollars.
16. A. 44
To be sure it never runs out, err on the big side: allow the most, 44 kg.
17. True
Rounded up, the estimate is 69; when it can't decide, work it out: 26.8 + 25.6 + 15.5 = 67.9, and compare with 69.
18. 4 notes
5 × 35.7 = 178.5, and 178.5 ÷ 50 rounded up is 4 notes.

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