An open box is made of wood 3 cm thick. Its external length, breadth and height are 1.48 m,1.16 m and 8.3 dm. Find the cost of painting the inner surface at Rs.50 per sq. metre.

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answer is A.

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Detailed Solution

Concept: To solve this question, first we have to calculate the internal dimensions of the box from the data provided in the question about the external dimensions. Then, we have to calculate the interior surface area of the box and multiply the value with the cost of painting per sq. metre. to obtain our desired answer.
We need to know the perimeter of a rectangular surface = 2(l+b)
Where, “l” is the length of the box and, “b” is the breadth of the box.
Also, we need to know the formula for interior 4 walls of a cuboidal box
= (Perimeter of the Box × h)…[Where, “h” is the height of the box]
= [2(l+b)×h]
And, Area of a rectangular section = (l×b).
For better understanding, let us visualise from diagrams.
Question Image

The above figure is the isometric view and below is the top view.
Question Image

Given are the external dimensions of the box,
external length 1. 48m, breadth 1. 6m, height 8. 3 cm or 0. 83 m and 3 cm thick or 0. 03m.
Question Image

Therefore, Total cost of painting the interior surface of the box at the cost of Rs 50 per sq. meter. is

Hence, the correct answer is (1).

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