Question

The areas of two concentric circles are $962.5c{m}^2$ and $1386c{m}^2$ respectively. The width of the ring is ___________.

• A. $3.4$cm
• B. $3.5$cm
• C. $3.2$cm
• D. $3.1$cm

Answer 1

Answer: (B)

$3.5$cm

Given the area enclosed by $2$ circles with radius $r_1,r_2$ are $962.5{cm}^2$ and $1386{cm}^2$ respectively.

$\therefore r_2>r_1$

Now, width of the ring is to be found out.

Also, $\pi r_2^2=1386=>r_2^2=1386\times \frac{7}{22}\therefore r_2=21cm$

And, $\pi r_1^2=962.5=>r_1^2=962.5\times \frac{7}{22}\therefore r_1=17.5cm$

Therefore, width of the ring is basically $21-17.5=3.5$cm