Question

13
the areas of two concentric circles forming a ring are 154 sq cm and 616 sq cm. The breadth of the ring is
(b) 14 cm
(c) 21 cm
(d) 28 cm
(a) 7 cm​

Answer 1

$\red{\textbf{Answer = (a) 7cm}}$

$\textsf{Breadth of the ring is equal to the}$

$\textsf{difference between the radius of the outer}$

$\textsf{circle and the radius of the inner circle}$

$\textsf{Given the area of outer circle=}$$616c {m}^{2}$

$\pi {r}^{2} _{2} = 616$

$\pi {r}^{2} _{2} = \LARGE \frac{616 \times 7}{22}$

$= 196$

∴$\textsf{and the area of the inner circle}$$154 {cm}^{2}$

$\pi {r}^{2} _{1} = 154$

$\pi {r}^{2} _{1} = \LARGE\frac{154 \times 7}{22}$

$= 49$

$r_{1} = 7cm$

∴$The \: required \: answer = r_{2} - \: r_{1}$

$= 14 - 7 = 7cm$

$\textsf{so, The breadth of the ring is 7cm}$

∴$\textsf{the answer is option (a)}$