P1 Hong Kong Coins: Paper 4 Error Clinic

2026-11-11

This paper targets the mistakes P1 pupils make most often with coins: comparing digits across units, writing only one digit for cents, borrowing in subtraction, forgetting to convert units after multiplying, and using too many coins.

Direct answers　Answers: 1 no, 200 cents is more than 150; 2 350 cents; 3 19 dollars; 4 13 dollars 10 cents; 5 6 dollars 90 cents; 6 14 dollars; 7 12 days; 8 11 dollars 60 cents; 9 3 coins; 10 it should be 650 cents.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: P1 Hong Kong Coins
Level	P1

02　Questions (10 items)

FoundationError clinic: someone says a 2-dollar coin is worth less than 150 cents. Is that right?
FoundationAn item costs 6 dollars 50 cents and you pay with 10 dollars. How many cents of change?
FoundationThree 5-dollar coins and two 2-dollar coins add up to how many dollars?
IntermediateWhat is 7 dollars 20 cents plus 5 dollars 90 cents?
IntermediateYou pay 20 dollars for an item costing 13 dollars 10 cents. How much change?
IntermediateEach pen costs 3 dollars 50 cents. How much do 4 pens cost?
ChallengeSaving 2 dollars 50 cents a day, how many days are needed to reach 30 dollars?
ChallengeThree books cost 12 dollars 80 cents each and you pay with 50 dollars. How much change?
ChallengeWhat is the fewest coins needed to make 1 dollar 70 cents using 1 dollar, 50 cent and 20 cent coins?
Error redoError clinic: someone writes 6 dollars 50 cents as 6 dollars 5 cents. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	No. 2 dollars is 200 cents, and 200 is more than 150.	Convert to the same unit before comparing; dollars and cents cannot be compared digit by digit.
2	350 cents, which is 3 dollars 50 cents. 1000 minus 650 is 350.	Change both amounts to cents first, then subtract.
3	19 dollars. 5 times 3 is 15, 2 times 2 is 4, and 15 plus 4 is 19.	Multiply within each group, then add the two groups.
4	13 dollars 10 cents. 720 plus 590 is 1310 cents.	Every 100 cents in the cents column carries 1 into the dollars column.
5	6 dollars 90 cents. 2000 minus 1310 is 690 cents.	Change both to cents so the borrowing step is safe.
6	14 dollars 00 cents. 350 times 4 is 1400 cents.	Multiply price by quantity, then turn cents back into dollars.
7	12 days. 3000 divided by 250 is 12.	Turn the target and the daily saving into cents before dividing.
8	11 dollars 60 cents. 1280 times 3 is 3840 cents, and 5000 minus 3840 is 1160 cents.	Find the total first, then the change; write the two steps separately.
9	3 coins: 100 plus 50 plus 20 is 170 cents.	Take the largest value first and top up with smaller ones.
10	It is wrong. 6 dollars 50 cents is 650 cents, while 6 dollars 5 cents is only 605 cents, a gap of 45 cents.	The cents part always has two digits, so 50 cents is never written as 5 cents.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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