The area of a circle of radius 4cm is equal to (Take π = 3.142 )

1. Analyze the question

We are asked to calculate the area of a circle given its radius ($r = 4\text{ cm}$) and a specific value for $\pi$ ($\pi = 3.142$).

2. Explain the concept

The area ($A$) of a circle is calculated using the formula:

Where:

• $\pi$ (pi) is a constant (given here as 3.142).
• $r$ is the radius of the circle.
• $r^2$ means the radius multiplied by itself ($r \times r$).

3. Show the solution

• Step 1: Identify the given values. • $r = 4\text{ cm}$ • $\pi = 3.142$
• Step 2: Substitute the values into the formula. • $A = 3.142 \times (4)^2$
• Step 3: Calculate the square of the radius. • $4^2 = 4 \times 4 = 16$
• Step 4: Multiply by $\pi$. • $A = 3.142 \times 16$ • $A = 50.272$

Rounding $50.272$ to one decimal place gives us $50.3\text{ cm}^2$.

4. Identify the answer

Comparing our result to the options provided: A. $10.3\text{ cm}^2$ B. $15.7\text{ cm}^2$ C. $50.3\text{ cm}^2$ D. $17.4\text{ cm}^2$

The correct option is C.

5. Exam Tip

When solving circle problems in JAMB, always check if the question specifies the value of $\pi$ to use (e.g., $3.142$ or $22/7$). Using the wrong one can lead to slight variations in your answer. Also, remember that Area is always measured in square units ($\text{cm}^2, \text{m}^2$), while Circumference is measured in linear units ($\text{cm}, \text{m}$).