Some coins of diameter 1.5 cm and thickness 0.2 cm are melted to form a right circular cylinder whose height is 8 cm and diameter is 6 cm. Find the number of coins –

Correct option is B

- Diameter = 1.5 cm → Radius = 1.5 / 2 = 0.75 cm
- Thickness (Height) = 0.2 cm
The volume of one coin is given by:
Volume of coin = π r² h
= π (0.75)² (0.2)
= π (0.5625) (0.2) = π × 0.1125
= 0.1125π cm³
The newly formed cylinder has:
- Diameter = 6 cm → Radius = 6 / 2 = 3 cm
- Height = 8 cm
The volume of the new cylinder is:
Volume of cylinder = π r² h
= π (3)² (8)
= π (9) (8) = 72π cm³
Number of coins required:
Number of coins = V_cylinder / V_coin
= (72π) / (0.1125π)
= 72 / 0.1125
= 640