If the length of a rectangle is decreased by 25% and the width is increased by 30%, then by what percent is the area of the rectangle decreased?
If the length of a rectangle is decreased by 25% and the width is increased by 30%, then by what percent is the area of the rectangle decreased?
If the length of a rectangle is decreased by 25% and the width is increased by 30%, then by what percent is the area of the rectangle decreased?
Let $a,b$ are the length and width of the original retangle, then we have the area is: $S=\frac{1}{2}ab$
We have:
$a'=0,75a$
$b'=1,3b$
So the area of a retangle after change is $S'=\frac{1}{2}a'b'=\frac{1}{2}.0,975.a.b$
So it's very easy calculating the percent of the area of the rectangle decreased is $2.5 \%$
Bài viết đã được chỉnh sửa nội dung bởi hoangtrong2305: 22-12-2013 - 20:26
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Let $a,b$ are the length and width of the original retangle, then we have the area is: $S=\frac{1}{2}ab$
We have:
$a'=0,75a$
$b'=1,3b$
So the area of a retangle after change is $S'=\frac{1}{2}a'b'=\frac{1}{2}.0,975.a.b$
So it's very easy calculating the percent of the area of the rectangle decreased is $2.5 \%$
Thanks you so much!
Bài viết đã được chỉnh sửa nội dung bởi thinhrost1: 27-12-2013 - 19:12
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