2021 · Q72
How many silver coins, 3.5 cm in diameter and of thickness 4 mm, must be melted to form a cuboid of dimensions 21 cm x 11 cm x 7 cm ? (take π = 22/7)
Elementary MathematicsMensuration
- A420
- B210
- C200
- D168
Explanation
One coin has volume π·(1.75)²·0.4 = 1.225π cm³; the cuboid has volume 21 × 11 × 7 = 1617 cm³. The number of coins is 1617/(1.225π) = 1617 × 7/(1.225 × 22) = 420. This is option (a).