The average age of 30 boys in a class is 15 years. One boy, aged 20 years, left the class, but two new boys came in his place whose age differs by 5 years. If the average age of all the boys now in the class becomes 15 years, the age of the younger newcomer is: 

Find the average of the following sets of numbers.

693, 456, 876, 532, 934, 691, 596, 398, 682

Average of 11 number is 30. If the average of first 10 numbers is 22, then find the 11th number?

The average of 20 numbers is 32. If two numbers are 29 and 31, then what is the average of the remaining numbers (correct up to two decimals)? 

What will be the average of the following set of scores?
59, 84, 44, 98, 30, 40, 58

In a school with 600 students the average age of the boys is 12 years and that of the girl is 11 years. If he average age of the students is 11 years 9 months, then the number of girls in the school is