The length of a rectangular blackboard is 8 m more than its breadth. If its length is increased by 7 m and its breadth is decreased by 4 m, its area remains unchanged. The length and breadth of the rectangular blackboard is :
Options:
A . 24 m, 16 m
B . 20 m, 24 m
C . 28 m, 16 m
D . 28 m, 20 m
Answer: Option D Let the breadth = x cm Then, length = (x + 8) m $$\eqalign{ & \therefore \left( {x + 8} \right)x = \left( {x + 15} \right)\left( {x - 4} \right) \cr & \Rightarrow {x^2} + 8x = {x^2} + 11x - 60 \cr & \Rightarrow x = 20 \cr} $$ So, length = 28 m and breadth = 20 m
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