The length of a rectangle is decreased by r% , and the breadth is increased by (r + 5)%. Find r , if the area of the rectangle is unaltered ..
Let original length = `x` and original breadth = y,
Then , original area = `xy`
New area = `[(100 - r)/100 xx x] [ (105 + r)/100 xx y]`
=`[(10500 - 5r - r^2)/(10000))xy]`
`:.` `((10500 - 5r - r^2)/(10000)) xy = xy`
`hArr r^2 + 5r - 500 = 0`
`hArr (r + 25 ) (r - 20)= 0`
`hArr r = 20`
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