A rectangular playground is 420 sq.m. If its length is increases by 7 m and breadth is decreased by 5 metres, the area remains the same. Find the length and breadth of the playground ?

12. A rectangular playground is 420 sq.m. If its length is increases by 7 m and breadth is decreased by 5 metres, the area remains the same. Find the length and breadth of the playground ?

Sol. Let the length of a rectangular playground be ‘x’ m.


∵  The area of playground is 420 sq.m.

∴ length × breadth = 420

∴ x(breadth) = 420

∴ breadth = 420/x metre.

New length = (x + 7) m

New breadth = (420/x  – 5) m

As per the given condition,

Area of new rectangle = Length × Breadth

420 = (x + 7) (420/x  – 5)

∴ 420 = 420 – 5x + 2940/x – 35

∴ 420 – 420 = - 5x + 2940/x – 35

∴ 0 = - 5x + 2940/x – 35

Multiplying by x, we get

0 =     - 5x2 + 2940 – 35x

∴ 5x2  + 35x – 2940 = 0

Dividing by 5, we get

x2 + 7x – 588 = 0

x2 – 21x + 28x – 588 = 0

x (x – 21) + 28 (x – 21) = 0

(x – 21) (x + 28) = 0

x – 21 = 0 or x + 28 = 0

x = 21 or x = -28

The length of playground cannot be negative.

∴ x = 21

420/x = 420/21 = 20


∴ The length of a rectangular playground is 21 m and its breadth is 20 m.