In order to keep the product of two numbers constant, what percent should one be diminished if other increases by 25%

The  year next to 1990 having the same calender as that of 1990 is:

A man goes 10m due north and then 30m due east. His distance from the starting place is:

A father is twice as old as his son 20 years ago, the age of the father was 12 times the age of the son. The present age of the son is.

If + means ÷, -means ×, ÷means + and ×means –, then 36×12+4÷6+2-3 =?

The ratio of milk and water in a mixture is 4:3. If 14 liters of water is added to the mixture, the ratio of milk and water become 3:4. Then the quantity of milk in the mixture is.