GRE General TestQuantitative ReasoningMedium
A civil engineer is calculating the required volume of concrete for a cylindrical pillar. The pillar has a diameter of 1.4 meters and a height of 5 meters. What is the volume of concrete needed, in cubic meters? (Use π ≈ 22/7)
- A77.0
- B7.7
- C154.0
- D38.5
Show answer & explanationAnswer & explanation
Correct answer: B. 7.7
The radius is half the diameter, so r = 0.7m. Volume of a cylinder V = πr²h. V = (22/7) * (0.7)² * 5 = (22/7) * 0.49 * 5 = 22 * 0.07 * 5 = 22 * 0.35 = 7.7 m³.
Why the other options are wrong
- A. This results from using the diameter instead of the radius and doubling it (πd²h * 2), or other calculation errors.
- C. This results from using the diameter instead of the radius and multiplying by 4 (πd²h * 4), or other calculation errors.
- D. This results from using the diameter instead of the radius (πd²h).
Volume of a Cylinder
The volume of a cylinder is the area of its circular base multiplied by its height.
- Formula: V = πr²h, where r is the radius and h is the height.
- Radius (r) is half of the diameter (d).
- Units for volume are cubic units (e.g., m³).
Memory trick: Radius Squared Times Pi, then by the Height.