There are 520 children at a playground in the morning. In the afternoon, 180 children leave. How many children are still at the playground? Use a mental calculation strategy.
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Worked Solution
Mental strategy — round and adjust:
Step 1: Round 180 up to 200 (add 20 extra).
Step 2: 520 − 200 = 320.
Step 3: We subtracted 20 too many, so add 20 back: 320 + 20 = 340.
Answer: 340 children.
Correct answer: 340
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