The average of three numbers is 40. The first number is twice the second and the second one is thrice the third number. The difference between the largest and the smallest numbers is

The average age of P, Q, R, and S is 30 years. How old is R?
I. The sum of ages of P and R is 60 years.
II. S is 10 years younger than R.

The average of 8 readings is 24.3, out of which the average of first two is 18.5 and that of next three is 21.2. If the sixth reading is 3 less than seventh and 8 less than eight, what is the sixth reading? 

The average age of students in a class is 15.8 years. The average age of boys in the class is 16.4 years and that of the girls is 15.4 years. The ratio of the number of boys to the number of girls in the class is:

In a class of 66 students there are 33 girls. The average weight of these girls is 61 Kg and average weight of the full class is 66 kgs. What is the average weight of the boys of the class?

The average weight of A B and C is 50 kg . if the average weight of A and B be 48 kg and that of B and C be 45 kg , then find the weight of B ?

The average of five numbers is  27.  If one  number is excluded. The average becomes 25. The excluded number is

The average of 12 number is 42. If a 13th number is added, then the average becomes 44. What is the 13th number?