# RD Sharma Solutions Class 7 Mathematics Solutions for Mensuration 1 Exercise 20.1 in Chapter 20 - Mensuration 1

Question 21 Mensuration 1 Exercise 20.1

A hall 36 m long and 24 m broad allowing 80 m2 for doors and windows, the cost of papering the walls at Rs 8.40 per m2 is Rs 9408. Find the height of the hall.

Given length of the hall = 36 m

Breadth of the hall = 24 m

Let h be the height of the hall.

Now, in papering the wall, we need to paper the four walls excluding the floor and roof

of the hall. So, the area of the wall which is to be papered = Area of 4 walls

= 2 h (I + b)

= 2 h (36 + 24)

= 120 hm^2

Now, area left for the door and the windows = 80 m^2

So, the area which is actually papered = (120h – 80) m^2

Cost of papering the wall = Area required for papering × Cost per meter square of

papering wall

9408 = (120 h – 80) × 8.40

1120 = 120 h – 80

1200 = 120 h

h = 10 m

Hence, the height of the wall would be 10 m.

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