The average of ten numbers is 72. The average of the first four numbers is 69 and that of the next three number is 74. The 8^th number is 6 more than the 9^th number and 12 more than the 10^th number. What is the average of the 8^th and 9^th numbers?

The average of 8 readings is 24.3, out of which the average of the 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 marks of the students of a class is 68. The average marks of girls in the class is 80 and that of boys is 60. What percentage of students are boys in the class?

What is the average of the first five prime numbers?

If the average marks of three batches of 55, 60 and 45 students respectively is 50, 55 and 60, then the average marks of all the students is?

There are 1600 students in a college, whose average weight is 50 kg. If average weight of boys is 54 kg. and average weight of girls is 38 kg. Then find the number of girls in the school.

The average salary of 12 employees in a company was recorded to be ₹20,000. If the salary of the manager is also included, then the average salary increases by ₹2,000. Find the salary of the manager.

The average weight of 8 people increase by 2.5 kg when a new person comes in place of one of them weighting 75 kg. What is the weight of the new person?