If the height of a right prism is increased by 50% and base area remains the same, what is the percentage increase in volume?
- (a)25%
- (b)50%
- (c)75%
- (d)100%
Answer
Why
Correct — B. Volume of a right prism = base area × height, and here only the height changes.
Old volume: V = A × h
Raise the height by 50%: h becomes 1.5h
New volume: A × 1.5h = 1.5V
Increase: 1.5V − V = 0.5V = 50% → option (b)
Why the others are wrong
- (a)25% — 25% is half the height change. With the base fixed, volume is directly proportional to height, so it rises by the full 50%.
- (c)75% — 75% would need the height multiplied by 1.75. With the base unchanged, the volume factor equals the height factor, 1.5.
- (d)100% — 100% means the volume doubles, which needs the height doubled. A 50% rise makes the volume 1.5 times, not 2 times.
Concept
For any right prism, volume = area of the base × height, whatever shape the base has. With the base fixed, volume is directly proportional to height.
So a percentage change in height passes straight through to volume. It is a change in a squared length, such as a cylinder's radius, that gets amplified: a 50% rise in radius multiplies volume by 1.5² = 2.25.
Key facts
- Volume of a right prism = base area × height.
- With the base fixed, a k% rise in height gives a k% rise in volume.
- A length that is squared in a volume formula scales the volume by the square of its factor.
Study next
Common traps
- Squaring the factor out of habit (1.5² = 2.25, a 125% rise) when only the height changes.
- Reading a 50% increase as a factor of 0.5 instead of 1.5.
12 Sep 2025, 16:00, Quant Q.21 also changes only the height: a triangular prism with base 25 cm² and height 10 cm has its height raised by 20%, keyed 300 cm³.
17 Sep 2025, 16:00, Quant Q.13 shows the squared case: a cone's radius rises 20% and its height falls 10%, keyed a 29.6% increase.
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