Question

The number of square stamps each of side 1 in x 1 in required to cover the whole box leaving the triangular face are .

• A. 280
• B. 360
• C. 420
• D. 480

Answer 1

The correct option is D 480

To find out the number of stamps required to cover the box, we will divide the area of the surface of box excluding the triangular faces by the area of the each stamp.

$\text{Area of each stamp =}1\times 1$
$=1sqin$

Area of triangular prism excluding the triangular faces is the area of its three lateral rectangle faces.

$\text{Area of lateral faces =}16\times 5+16\times 12+16\times 13$
= 80 + 192 + 208
= 480 sq in

$\text{Number of stamps pasted =}\frac{\text{Area of the surface}}{\text{Area of stamp}}$

$=\frac{480}{1}$
$=480$
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∴ Number of stamp that can be pasted to cover the box are 480.