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The length and the breadth of a rectangular door are increased by 1 m each and due to this the area of the door increased by 21 sq. m. But if the length is increased by 1 m and breadth decreased by 1 m, area is decreased by 5 sq. m.
Find the perimeter of the door.

A. 20 m
B.25 m
C.40 m
D.30 m
Answer and Feedback
Answer:C
Feedback:Let original length = l, breadth = b, so area = lb
When l and b increased by 1:
(l+1)(b+1) = lb + 21
Solve, l + b = 20
When l increased by 1, b decreased by 1:
(l+1)(b-1) = lb – 5
Solve, l – b = 6
Now solve both equations, l = 13, b = 7
Perimeter = 2(13+7) = 40

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