The radii of two circles are ^@ 20 \space cm ^@ and ^@ 9 \space cm ^@ respectively. Find the radius of the circle which has its circumference equal to the sum of the circumference of the two circles.
Ria is always curious in creating formulas, for solving mathematical problems, of her own by repeated trial and error method. One day she found a formula for finding the surface area of the hexagonal pyramid. What should be the correct formula for the surface area of the hexagonal pyramid?
There are a total of 16 chocolates - 4 each in the flavors of mango, banana, grape and orange. There are also 5 children. If each child is allowed to choose their own favorite flavor, what is the probability that all of them will get flavors of their choice?