30 + 40 ≠ 10. That would be 40 − 30. Add the tens: 3 + 4 = 7, so 30 + 40 = 70.
PRIMARY 1 · MATHEMATICS
Addition and Subtraction
Top 5 mistakes
Ranked by how often they appear across 30 MOE-aligned practice questions in our archive.
34 = 30 + 4. But the sum is 30 + 40, not 30 + 4. 70 is correct.
74 = 70 + 4. But 30 + 40 = 70 only. There are no extra ones.
15 is the total after buying. The starting number is 9, and he buys 6: 9 + 6.
Sam already has 9 and gets 6 more. 9 + 6 = 15 is the correct sentence.
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