Question

Fig. 11 3.9 The length of a rectangle exceeds its breadth by 5 cm. If the breadth and the length are decreased by 10%, what will be the percentage change in its perimeter?
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Answer 1

Answer:

Let breadth be B, then length =L=B+5

If they are decreased by 10% , then new values are breadth b=B(1-10/100)=0.9B and length=0.9L

original perimeter=2(L+B)=2(B+5+B)=2(2B+5)

new perimeter=2×0.9(2B+5)=1.8(2B+5)

change in perimeter=0.2(2B+5)

% change=[{0.2(2B+5)}/{2(2B+5)}]×100=10%