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 :

A. 24 m, 16 m

B. 20 m, 24 m

C. 28 m, 16 m

D. 28 m, 20 m

Answer: Option D

Solution(By Examveda Team)

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