Question

A water tank has two faces congruent isosceles trapeziums and the other faces rectangles. Its dimensions are as shown below:

What would be the cost of painting its inside and out at the rate of 75 rupees per square metre?

Answer 1

Height of the water tank = 0.4 m

Length of the rectangular base = 1.4 m

Breadth of the rectangular base = 0.7 m

Base perimeter = 2 (Length + Breadth)

= 2 (1.4 + 0.7) m

= 4.2 m

Lateral surface area of the water tank = Base perimeter × Height

= (4.2 × 0.4) m²

= 1.68 m²

Area of the rectangular base = Length × Breadth

= (1.4 × 0.7) m²

= 0.98 m²

Surface area of the water tank = Lateral surface area + Area of the rectangular base

= (1.68 + 0.98) m²

= 2.66 m²

Area to be painted = 2 × Surface area of the water tank

= 2 × 2.66 m²

= 5.32 m²

Cost of painting per sq. metre = Rs.75

∴ Cost of painting 5.32 m² area = Rs.75 × 5.32 = Rs.399