Two circles of same radius intersect each other at P and Q. If the length of the common chord is 30 cm and distance between the centres of the two circlesis 40 cm, then what is the radius (in cm) of the circles?
A boat goes 15 km upstream and 10 1/2 km down stream in 3 hrs 15 min. It goes 12 km upstream and 14 km downstream in 3 hrs. What is the speed of the boat in still water?