It looks like the tens column was skipped. Only the hundreds (2 + 1 = 3) and units (4 + 8 = 12, write 2 carry 1) were added, giving 302. Always work through every column: units, tens, then hundreds.
PRIMARY 2 · MATHEMATICS
Addition and Subtraction
Top 5 mistakes
Ranked by how often they appear across 18 MOE-aligned practice questions in our archive.
You added the units correctly (4 + 8 = 12, write 2 carry 1), but forgot to add the carried 1 to the tens column. 3 + 5 = 8, not 9. Always remember to add the carry to the next column.
You correctly carried 1 from the units to the tens (3 + 5 + 1 = 9), but then carried an extra 1 into the hundreds column by mistake. There is no carry from the tens here, so hundreds = 2 + 1 = 3, not 4.
You rounded 39 up to 40 and got 75 − 40 = 35. But then you subtracted 1 again instead of adding it back. When you over-subtract by rounding up, you must add back the difference. 35 + 1 = 36, not 34.
You rounded 39 up to 40 and subtracted correctly: 75 − 40 = 35. But then you added 9 back instead of 1. When you round up by 1, you only add back 1, not the whole rounded amount. 35 + 1 = 36.
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