Question

A cylinder has radius $7\text{ cm}$ and height $10\text{ cm}$. Find its curved surface area. [$\text{CSA} = 2\pi rh$]

• A. $220\text{ cm}^2$
• B. $440\text{ cm}^2$
• C. $560\text{ cm}^2$
• D. $770\text{ cm}^2$

Hint:

When the radius is a multiple of 7, always use $\pi = \frac{22}{7}$ instead of $3.14$ to make the calculation much faster and cleaner!

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The curved surface area (CSA) of a cylinder represents the area of the side surface, excluding the top and bottom circular bases.

Step 2: Identifying the Formula and Values:
The formula is: $\text{CSA} = 2\pi rh$ Given:
• Radius ($r$) = $7\text{ cm}$
• Height ($h$) = $10\text{ cm}$
• $\pi \approx \frac{22}{7}$

Step 3: Calculation:
\[ \text{CSA} = 2 \times \frac{22}{7} \times 7 \times 10 \] The $7$ in the numerator and denominator cancel out: \[ \text{CSA} = 2 \times 22 \times 10 \] \[ \text{CSA} = 44 \times 10 = 440\text{ cm}^2 \]

Step 4: Final Answer:
The curved surface area is $440\text{ cm}^2$.