Question

1) Area of rectangular playground is 420 sq.m. if the length of
a playground is increased by 7 meter and breadth is decreased
of by 5 meter; area remain unchanged then find the length
and the breadth.
1​

Answer 1

Answer:

Step-by-step explanation:

Let the length of the playground be  

l  and breadth be  b

Thus,  l b = 420

 ∴ l = 420 /b ......(1)

Length is increased by  7 m

and breadth is increased by  5 m

∴ ( l + 7 ) ( b − 5 ) = 420

( 420/b + 7 ) ( b − 5 ) = 420 ........From (1)

( 420 + 7 b ) ( b − 5 ) = 420 b

420 b + 7 b^ 2 − 35 b − 2100 = 420 b

7 b ^2 − 35 b − 2100 = 0

b ^2 − 5 b − 300 = 0

b ^2 − 20 b + 15 b − 300 = 0

( b − 20 ) ( b + 15 ) = 0  

b = 20 , − 15

Taking only positive value of  b

Thus,  l = 420 /20 = 21 m

Hence, length  = 21 m

and breath  = 20 m

hope it helps..