We are given that diameter of base = 8 ft. Therefore, the radius of circular base = 8/2 = 4 ft
In triangle OAB and OCD
OA/AB = OC/CD
⇒ AB = 3×4/12 = 1ft
Therefore, the volume of remaining part = Volume of entire cone - Volume of smaller cone
⇒ 1/3×π×42×12-1/3×π×12×3
⇒ 1/3×π×189
⇒ 22/7×3×189
⇒ 198 cubic ft
\(M\) is the centre of the circle. \(l(QS) = 10\sqrt{2}\), \(\ell(PR) = \ell(RS)\) and \(PR \perp QS\). Find the area of the shaded region. (\(\pi = 3\))}

Three circles, each of radius 20, have centres at P, Q, and R. Further, AB = 5, CD = 10 and EF = 12. What is the perimeter of \( \triangle PQR \)?