Question

1. Three cubes of silver with edges 3 cm, 4 cm and 5 cm are melted and recast into a single
cube. Find the cost of coating the surface of the new cube with gold at the rate of 3.50
per square centimetre.​

Answer 1

Let’s consider a cm to be the edge of new cube

Then, according to given conditions in the question

a3 = 33 + 43 + 53

= 27 + 64 + 125

= 216 cm³

a = ³√216

∴ a = 6 cm

So, the surface area of new cube = 6 × (side)²

= 6 × (6)²

= 216 cm²

Hence,

the cost of coating the surface of new cube = ₹3.50 × 216 = ₹156

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