JAMB 2015 Mathematics · Question 14

The volume of a cone (s) of height 6cm and base radius 5cm is

Options

  1. A.157cm3
  2. B.155cm3
  3. C.175cm3
  4. D.145cm3

Answer: A. 157cm3

Explanation written with AI and checked against the answer key

1. Analyze the question

We are asked to calculate the volume of a cone given its height (hh) and base radius (rr).

  • Height (hh) = 6 cm
  • Radius (rr) = 5 cm
  • We will use π≈3.142\pi \approx 3.142 (standard for JAMB calculations unless specified as 22/722/7).
2. Explain the concept

The volume (VV) of a cone is given by the formula:

V=13πr2hV = \frac{1}{3} \pi r^2 h

Where:

  • π\pi (pi) is a constant (approximately 3.142 or 22/7)
  • rr is the radius of the circular base
  • hh is the perpendicular height of the cone
3. Show the solution

Step 1: Substitute the values into the formula.

V=13×π×(5)2×6V = \frac{1}{3} \times \pi \times (5)^2 \times 6

Step 2: Simplify the expression. First, calculate the square of the radius:

52=255^2 = 25

Now, substitute back:

V=13×π×25×6V = \frac{1}{3} \times \pi \times 25 \times 6

Step 3: Perform the arithmetic. You can simplify 13×6\frac{1}{3} \times 6 first, which equals 2:

V=π×25×2V = \pi \times 25 \times 2
V=50πV = 50\pi

Step 4: Calculate the final numerical value. Using π≈3.14159...\pi \approx 3.14159...

V=50×3.14159V = 50 \times 3.14159
V=157.079... cm3V = 157.079... \text{ cm}^3

Rounding to the nearest whole number, we get 157 cm³.

4. Identify the answer

Comparing our result to the given options, it matches option A.

5. Tip

In JAMB Mathematics, if you see π\pi in the options, leave your answer in terms of π\pi. If the options are whole numbers, use 3.1423.142 for π\pi to get the most accurate result. Also, remember that the volume of a cone is exactly one-third the volume of a cylinder with the same radius and height (Vcylinder=πr2hV_{cylinder} = \pi r^2 h).

AI can make mistakes. Report anything that looks wrong.

Past questions © the examination body (JAMB/WAEC/NECO). DeeepSolve is not affiliated with them. Rights holders: see /copyright.