The length of a class room floor exceeds its breadth by 25 m. The area of the floor remains unchanged when the length is decreased by 10 m but the breadth is increased by 8 m. The area of the floor is

• A. 4987 sq.m
• B. 4870 sq.m
• C. 5100 sq.m
• D. 4442 sq.m

Answer: (C)

Let the breadth of floor be 'b' m. Then, length of the floor is 'l = (b + 25)' Area of the rectangular floor = l x b = (b + 25) × b According to the question, (b + 15) (b + 8) = (b + 25) × b b 2   +   8 b   +   15 b   +   120   =   b 2   +   25 b 2b = 120 b = 60 m. l = b + 25 = 60 + 25 = 85 m.   Area of the floor = 85 × 60 = 5100 sq.m.