Question

the length of a rectangle is 5/7 of its breadth. if its perimeter is 48cm then what is its length

Answer 1

let the b=x

perimeter of rectangle=2(l+b)
48=2(5/7×x+×)
48=2(5x/7+x/1)
48=2(5x/7+x×7/1×7)
48=2(5x/7+7x/7)
48=2(12x/7)
48/2=12x/7
24×7=12x
168=12x
168/12=x
14=x

now length = 5/7×14=5×2=10cm.
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Answer 2

let length of rect be x
5/7x = b
2(l+b) = 48cm
2(x+5/7x) = 48
x+5/7x = 48/2
taking LCM of LHS
(7x+5x)/7 = 24
12x = 24×7
12x = 168
x = 14
so length of rect = 14cm
breadth = 14×5/7
=10cm