What is the mean of the first five prime numbers?

There are 13 members in group A, 10 members in group B and 45 members in group C. All the members of these groups went to a restaurant. The average amount spent on each member of group A, B and C is Rs. 367, Rs. 112 and Rs. 401, respectively. The total average amount (in Rs. ) spent per member is:

In an experiment, the refractive index of water was found to be 1.35, 1.29, 1.32 and 1.36. What is the average refractive index of water?

The average age of 26 students of a class is 43 years. If the age of the teacher is also included, the average age of the whole group becomes 44 years. The age (in years) of the teacher is:

The average of 21 numbers is 74. The average of the first 11 numbers is 72.8 and that of the last 11 numbers is 77.2. If the 10th number is five less than the 11th number and if 10th and 11th numbers are excluded, then what is the average of the remaining numbers? (correct to nearest integer)