A cone and a cylinder have the same base radius and the same height. What is the ratio of the volume of the cone to the volume of the cylinder?
- (a)1:2
- (b)1:3
- (c)1:4
- (d)1:6
Answer
Why
Correct — B.
Rule: a cone holds one-third of the cylinder with the same base and height.
Cone: V = (1⁄3)πr²h
Cylinder: V = πr²h
Ratio = (1⁄3)πr²h : πr²h
Cancel πr²h → 1⁄3 : 1 = 1 : 3 → option (b).
Why the others are wrong
- (a)1:2 — 1 : 2 would make the cone half the cylinder. The cone formula carries 1⁄3, not 1⁄2, so the ratio is 1 : 3.
- (c)1:4 — 1 : 4 cannot come from these formulas. With the same r and h, πr²h cancels completely and leaves 1⁄3 : 1.
- (d)1:6 — 1 : 6 is the ratio for a cone half the cylinder's height, (1⁄3)πr²(h⁄2) : πr²h. Here the heights are equal, so it stays 1 : 3.
Concept
Both solids stand on the same base area, πr². A cylinder carries that area straight up through height h. A cone tapers from it to a point, and the taper costs it two-thirds of the volume: V = (1⁄3)πr²h.
So when r and h match, the ratio is fixed at 1 : 3 whatever the actual sizes. Put the other way, three such cones of water fill the cylinder.
Key facts
- Volume of a cone = (1⁄3)πr²h.
- Volume of a cylinder = πr²h.
- With equal radius and height, cone : cylinder = 1 : 3.
Study next
Common traps
- Inverting the ratio to 3 : 1, which answers cylinder to cone
- Looking for sizes the question never gives, when πr²h cancels and the ratio needs none
26 Sep 2024, 16:00, Quant Q.3 uses the same (1⁄3)πr²h directly: a cone of radius 3.5 cm and height 18 cm, keyed 231 cm³.
17 Sep 2025, 16:00, Quant Q.13 raises a cone's radius by 20% and cuts its height by 10%, keyed a 29.6% increase.
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