數學題唔識??

The volume of water in a pool was increased by 20% in July, then decreased by 5% in August and increased by 25% September. What was the overall percentage change in the volume of water between the beginning of July and the end of September?
let x be the beginning of July
overall percentage change=
[{[x(1+20%)(1-5%)(1+15%)]-x}/x]*100%
=[(1.425x-x)/x]*100%
=0.425*100%
=42.5%
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2008-09-15 15:50:29 補充：
悠閒舒適™ 兄係唔係睇錯左between Aug and Sept??
真係唔小心><"

2008-09-25 21:14:13 補充：
發問者： chun_1209 ( 小學級 5 級)
2008-09-15 15:40:15 補充
答案係42.5%

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