Question

The length of a rectangular blackboard is 8 cm more than its breadth .If its length is increased by 7 cm and breadth is decreased by 4 cm ,its area remains unchanged .Find the length and breadth of the rectangular blackboard?​

Answer 1

Answer:

L= 28

B= 20

Step-by-step explanation:

L= 8+B

L'= (8+B)+7 = 15+B

B'= B-4

Area is same

L x B = L' x B'

(8+B)B = (15+B) (B-4)

3B =60

B=20

L=8 +20

Answer 2

Answer:

Let the length be L and breadth be B

Given, L=8+B

Area of the board, L×B=(8+B)×B

Given, If its length is increased by 7 cm and breadth is decreased by 4 cm, its area remains unchanged.

⇒(L+7)(B−4)=L×B

But L=8+B

⇒(8+B+7)(B−4)=(8+B)×B

⇒(15+B)(B−4)=(8+B)×B

⇒15B−60+B

2

−4B=8B+B

2

3B=60

B=20 cm

So, Length =20+8=28 cm

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