The average of the eight numbers 6, 11, 9, x, 8, 10, 7, 13 is 10. What is the value of x?

If the average of m numbers is n*n and that of n numbers is m*m , then the average of m+n numbers is

The average of 7 consecutive numbers is 20. What is the largest of these numbers?

The average of the first 8 numbers is 42. The average of the first 4 numbers is 40, and the average of the next 3 numbers is 44. What is the 8th number?

If x is the average of 1², 2², 3², ..., 10² and y is the average of first 10 even natural numbers, then y is what percent of x − y?

The average of all prime numbers between 60 and 80 is: