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Question -

How many coins 1.75 cm in diameter and 2 mm thick must be melted to forma cuboid 11 cm x 10 cm x 7 cm? 



Answer -

Given,

Diameter of the coin =1.75 cm

So, its radius =1.74/2 = 0.875 cm

Thickness or theheight = 2 mm = 0.2 cm

We know that,

Volume of the cylinder(V1) = πr2h

= π 0.8752 ×0.2

And, the volume of thecuboid (V2) = 11 × 10 × 7 cm3

Let the number ofcoins needed to be melted be n.

So, we have

V2 = V1 ×n

11 × 10 × 7 = π 0.8752 ×0.2 x n

11 × 10 × 7 = 22/7 x0.8752 × 0.2 x n

On solving we get, n =1600

Therefore, the numberof coins required are 1600

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