Question

the perimeter of a rectangle is 240 cm if its length is decreased by 10℅ and its breath increased by 20℅ we get the same perimeter find the length and breadth of the rectangle

Answer 1

P = 240 cm
2 × (l1 + b1) = 240
l1 + b1 = 240 : 2
l1 + b1 = 120
l1 = 120 - b1

l2 = 90% × l1
l2 = 0,9l1

b2 = 120% × b1
b2 = 1,2b1

P = 240
2 × (l2 + b2) = 240
l2 + b2 = 240 : 2
0,9l1 + 1,2b1 = 120
0,9 × (120 - b1) + 1,2b1 = 120
108 - 0,9b1 + 1,2b1 = 120
108 + 0,3b1 = 120
0,3b1 = 120 - 108
0,3b1 = 12
b1 = 12 : 0,3
b1 = 40 cm

l1 = 120 - b1
l1 = 120 - 40
l1 = 80 cm

The length of the rectangle = 80 cm
The breadth of the rectangle = 40 cm