A tank is filled by three pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. the second pipe fills the tank 5 hours faster than the first pipe and 4 hours slower than the third pipe. the time required by the first pipe is:

The present age of Sarita is five times the age of her son. Five years ago her age was $25$ times the age of her son at that time. What is Sarita's present age?

A cistern has two pipes. One can fill it with water in $8$ hours and other can empty it in $5$ hours. In how many hours will the cistern be emptied, if both the pipes are opened together when  $\frac{3}{4}$ of the cistern is already full of water.

Two trains A and B are running on parallel tracks in the same direction. Train A which is coming from behind takes 50 seconds to cross B completely. One person in train A observes that he crosses train B in 30 seconds. If the speed of the train A and train B is in the ratio of 2 : 1, what is the ratio of their lengths?

A person's present age is two-fifth of the age of his mother. After $8$ years, he will be one-half of the age of his mother. How old is the mother at present?