The curved surface area of a cylinder 5cm high is 110cm2. Find the radius of its base π = $\frac{22}{7}$

1. Analyze the question

We are given:

• Height of the cylinder ($h$) = 5 cm
• Curved surface area ($A$) = 110 cm²
• Value of $\pi$ = $\frac{22}{7}$
• We need to find the radius ($r$) of the base.

2. Explain the concept

The curved surface area of a cylinder is the area of the side (the "label" part of a tin). The formula for the curved surface area of a cylinder is:

Where:

• $A$ = Curved surface area
• $\pi$ = Pi (constant)
• $r$ = Radius of the base
• $h$ = Height of the cylinder

3. Show the solution

Substitute the given values into the formula:

Simplify the right side:

To solve for $r$, multiply both sides by the reciprocal of $\frac{220}{7}$ (which is $\frac{7}{220}$):

Divide 110 and 220:

4. Identify the answer

Comparing our result to the options provided: A. 2.6cm B. 3.5cm C. 3.6cm D. 7.0cm

The correct option is B.

5. Tip

When dealing with geometry problems involving $\pi = \frac{22}{7}$, always look for numbers in the equation that are multiples of 11 or 7. This often allows you to cancel out terms early, making your calculation much faster and reducing the risk of arithmetic errors during your JAMB exam!