A fruit vendor recovers the cost of 95 oranges by selling 80 oranges. What is his profit percentage?

If cosecθ - cotθ = \({1 \over a}\), then \( {a^2-1 \over a^2+1}\) is

Pipes A and B can fill a tank in 16 hours and 24 hours, respectively, whereas pipe C can empty the full tank in 40 hours. All three pipes are opened together, but pipe C is closed after 10 hours. After how many hours will the remaining part of the tank be filled ?

A motorboat whose speed is 20 km/h in still water takes 30 minutes more to go 24 km upstream than to cover the same distance downstream. If the speed of the boat in still water is increased by 2 km/h, then how much time will it take to go 39 km downstream and 30 km upstream?