Question

the diameter of a circle is 21 cm. find its area to the nearest whole number.

Explanation:

Step1: Find the radius

The radius $r$ of a circle is half of the diameter $d$. Given $d = 21$ cm, so $r=\frac{d}{2}=\frac{21}{2}=10.5$ cm.

Step2: Calculate the area

The formula for the area $A$ of a circle is $A=\pi r^{2}$. Substitute $r = 10.5$ cm into the formula: $A=\pi\times(10.5)^{2}=\pi\times110.25$. Using $\pi\approx3.14$, we have $A\approx3.14\times110.25 = 346.185$ $cm^{2}$.

Step3: Round to the nearest whole number

Rounding $346.185$ to the nearest whole number gives $346$ $cm^{2}$.

Answer:

$346$ $cm^{2}$