Question

A water tank of dimensions 2m * 3m * 1.5m is to be painted leaving its base. Find the total cost of painting the tank if rate of painting = ₹20/m^2.

(a) ₹540

(b) ₹500

(c) ₹420

(d) ₹400

This question was addressed to me during a job interview.

My doubt is from Surface Area of a Cuboid and a Cube in chapter Surface Areas and Volumes of Mathematics – Class 9

Answer 1

Right answer is (c) ₹420

To elaborate: For the tank, l = 2m, b = 3m and h = 1.5m (given).

The total area of the tank = 2{(2*3) + (3*1.5) + (2*1.5)}

= 2{13.5}

= 27 m^2

But it is given that all sides except the base are to be painted.

Hence, total area to be painted = 27 – (2*3)

= 21 m^2

Now, the cost of painting 1 m^2 = ₹20

Hence, the cost of painting 21 m^2 = 21 * 20 = ₹420.