Ahmad worked out 537 + 286 mentally during a school maths quiz at his Tampines primary school. He added the hundreds first, then the tens, then the ones, regrouping as he went. What is the correct sum?
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Worked Solution
Step 1: Decompose 286 into 200 + 80 + 6 to make mental addition easier.
Step 2: Add the hundreds first: 537 + 200 = 737.
Step 3: Add the tens next: 737 + 80 = 817 (because 737 + 60 = 797, then + 20 = 817; or 737 + 80 directly).
Step 4: Add the ones last: 817 + 6 = 823.
Step 5: Check by reverse subtraction: 823 − 286 = 537. ✓
Final answer: 823.
Answer: 823
Correct answer: 823
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