Volume of a right circular cylinder Find the volume (in cm³) of a right circular cylinder with diameter 21 cm and height 10 cm.
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A3118
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B3275
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C3621
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D3465
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ENone of these
Answer
Correct Answer: 3465
Explanation
Introduction / Context:The volume of a cylinder is V = π r^2 h. With a given diameter, we first halve it to get the radius, square it, and multiply by height and π.
Given Data / Assumptions:
- Diameter = 21 cm ⇒ radius r = 10.5 cm
- Height h = 10 cm
- Use π = 22/7 for an exact integer outcome.
Concept / Approach:Compute r^2, then apply V = π r^2 h. Keeping π as 22/7 simplifies to an exact value when r is a half-integer compatible with 7.
Step-by-Step Solution:
r^2 = 10.5^2 = 110.25 V = (22/7) * 110.25 * 10 = (22/7) * 1102.5 = 3465 cm^3Verification / Alternative check:Using π ≈ 3.14 yields ≈ 3462 cm³, which rounds to the exact 3465 obtained with 22/7—options list the exact value.
Why Other Options Are Wrong:3118, 3275, 3621 do not match π r^2 h with r = 10.5 and h = 10; only 3465 does.
Common Pitfalls:Using diameter in place of radius (forgetting to halve) or squaring 21 instead of 10.5 leads to large errors.
Final Answer:3465