Adam who is 20 years old is 4 times as old as Mary. What will be Mary’s age when Adam is twice as old as her?

The following equation is incorrect. Which two signs should be interchanged to correct the equation?
12 + 10 - 28 ÷ 7 x 4 = 48

If P means -, Q means +, R means x and  S means ÷ then what is the value of  8 R6S3Q5P9 

The total age of a mother and her son is 60 years. The difference between their ages is 30 years. Find out the age of the mother.

If -4$1 = 4, 7$-7 = 49 and 3$1 = -3, then find the value of -8$-5 = ?

Study the following information carefully and answer the questions given below:
There are six persons of different weights. Three persons are heavier than Rohan. Two person’s weight is in between Sohan and Geeta. Rajesh is heavier than Rakesh but lighter than Ram. Neither Rakesh nor Geeta is lightest person. Weight of 2nd heaviest person is 66kg. Weight of all persons are in whole numbers. What is the weight of Sohan?

Which of the following least number can be subtracted from 2486 to make it a perfect square?

The average age of father and his son is 22 years. The ratio of their ages is 10 : 1 respectively. What is the age of the son?