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求答案～ 不要看我写的～ 可能错的～ 谢谢～ 不要解方程～
Solution:
Total height of 12 children is 12 × 141.5 cm = 1698 cm.
Change in height for 12 children = 12 × 143 - 1698 = 18 cm.
Change in height for remaining children = 18 cm.
Number of remaining children = 18 ÷ (145 - 143) = 9.
Total number of children at first = 12 + 9 = 21.
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Ans : 21.