Question

The length. breadth and height of a room is 5m. 4m and 3m. The cost of white washing its four
walls at the rate of Rs. 7.50 per m ² is :
(a) Rs. 110 (b) Rs. 109 (c) Rs. 220 (d) Rs. 105​

Answer 1

Given:

The length, breadth and height of a room are 5m, 4m and 3m.

To find:

The cost of whitewashing its four walls at the rate of Rs. 7.50 per m ² is?

Solution:

The dimensions of the room:

Length = 5 m

Breadth = 4 m

Height = 3 m

We know,

$\boxed{\bold{Area \:of\:a\:4\:wall = L.S.A \:of\:a\:room = 2h (l + b)}}$

By using the formula above, we get

The area of 4 walls of the room is,

= Lateral surface area of the room

= 2h (l + b)

= 2 × 3 × (5 + 4)

= 6 × 9

= 54 m²

Now,

If the cost of whitewashing 1 m² of the 4 walls of the room is = Rs. 7.50

Then,

The cost of whitewashing 54 m² of 4 walls of the room is,

= Rs. 7.50/m² × 54 m²

= Rs. 405

Thus, the cost of whitewashing the four walls of the room at the rate of Rs. 7.50 per m ² is → Rs. 405.

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