f.2maths,,Rercentage~help

2008-02-21 3:23 am

要有列式...
1)The length and the eidth of a rectangular carpet have decreased by 10% and 7% respectively after washin.Find the percentage decreased in the area of the carpet.
2)Anthony's weight increased by 5% last month but has decreased by 5% this month.What is the percentage change in Anthony's weight in these two months?

回答 (1)

shucheong2005

2008-02-21 6:04 am

✔ 最佳答案

1.let x be the length,y be the width,a be the original area and A be the new area,
xy=a
A=(1-10%)x乘(1-7%)y
=0.9x乘0.93y
=(0.9)(0.93)(x)(y)
=0.837(xy)
因為xy=a
所以A=0.837a
%decrease:(1-0.837)*100%=16.3%

2.let x be the original weight
x*(1+5%)=1.05x
1.05x*(1-5%)=1.05x*0.95=0.9975x
% decrease=(1-0.9975)*100%=0.25%

3.let the original yield per unit area be x,the original size of farm be a,the original total yield be y and the new total yield be Y
xa=y
Y=(1-20%)a乘(1+30%)x
=(0.8a)(1.3x)
=1.04(ax)
Y=1.04y
%increase=(1-1.04)*100%=4%

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