数学题：要将糖和水按5：100的比配制成糖水，那么40克的糖需要多少克水？

数学题解答：这题可以正比例知识列方程解答。

设需要x克水。

5:100 = 40:x

5x = 100×40

5x=4000

x=800

答：40克糖需要800克水。

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