There is a circular park of radius 4 meters. Three friends Isa, Jamila, and Dawood are sitting at equal distance on its boundary each having a toy telephone (connected using strings) in their hands to talk to each other. Find the length of the string between a pair of the telephones.

A sphere is just enclosed inside a right circular cylinder. If the curved surface area of the cylinder is 30 cm^{2}, find the surface area of the sphere.

Jamila and Jalila each have a bag that contains one ball each of the colors blue, black, red, green and yellow. Jamila randomly selects a ball from her bag and puts it in Jalila's bag. Then Jalila randomly selects a ball from her bag and puts it in Jamila's bag. What is the probability that after this the contents of the bag are the same as before?

The price of diamond varies directly as square of its weight. The price of a 15 decigrams diamond is BD11250. If diamond breaks into two pieces whose weights are in the ratio 3:2, find the loss incurred.

In an exam with two subjects, 65% candidates passed the first subject, 75% candidates passed the second subject and 25% candidates failed in both the subjects. If 617.5 candidates passed in both subjects, then how many candidates wrote the exam?