1.  The length of a rectangle is twice its breadth. If its length is decreased by 5 cm and the breadth is increased by 5 cm, the area of the rectangle is increased by 75 cm2 . Therefore , the length of the rectangle is ?
A. 20 cm
B. 30 cm
C. 40 cm
D. 50 cm

Answer: Option C

Explanation:

Let breadth = b, length = 2b

∴ Area of rectangle = 2b x b

= 2b2

As per question.

∵ (2b - 5 ) (b + 5 ) = 2b2 + 75

⇒ 5b = 75 + 25

⇒ 5b = 100

∴ b = 100 / 5 = 20

Hence, length of the rectangle =2b

= 2 x 20

= 40 cm.