The perimeter of a square field is 10 cm more than the perimeter of a rectangle. The length of the rectangle is 60 cm which is 80% of its width. If a street of width 10 cm surrounds from outside the square, then find the total cost of constructing the street at the rate of Rs. 20 per sq.
cm.

Let the width of the rectangle = x cm Then, 80% of x = 60 x = 60 × 100/80 = 75 cm Perimeter of the rectangle = 2 (length + width) = 2 × (60 + 75) = 270 cm Perimeter of the square = (270 + 10) = 280 cm The sides of the square = 280/4 = 70 cm The area of the square field without street = (70)² sq. cm = 4900 sq. cm   The area of the square field with street = (70 + 20)² sq. cm = 8100 sq. cm The area of the street = 8100 – 4900 = 3200 sq. cm The total cost of constructing the street = 3200 × 20 = Rs. 64000