# RD Sharma Solutions Class 8 Mathematics Solutions for Volume Surface Area Cuboid Cube Exercise 21.3 in Chapter 21 - Volume Surface Area Cuboid Cube

Question 16 Volume Surface Area Cuboid Cube Exercise 21.3

A classroom is 7 m long, 6 m broad and 3.5 m high. Doors and windows occupy an area of 17 m2. What is the cost of white washing the walls at the rate of Rs 1.50 per m2?

Answer:

Given details are,

Dimensions of class room = 7m × 6m × 3.5m

Where, Length = 7m, Breadth = 6m, Height = 3.5m

Area of four walls (including doors & windows) = 2 (lh + bh) m2

= 2 (7×3.5 + 6×3.5)

= 91m2

Area of four walls (without doors & windows) =

Area including doors & windows – area occupied by doors & windows

= 91 – 17 = 74 m2

Then,

Cost for white washing 1m2 area of walls = Rs 1.50

∴ Total cost for white washing the walls = 74 × 1.50 = Rs 111

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