What is the average of the first five prime numbers?

What is the average of all odd natural numbers less than 100?

The average weight of 5 men is increased by 4 kg. If one of them who weigh 121 kg is replaced by another man, then what is the weight of the new man? 

The average of 10 numbers is 14. If each number is multiplied by 6 then what will be the new average?

The average of 11 numbers is 7. If each number is doubled, what will be the new average of the numbers?

A batsman scored 87 runs in the 21st match in his career. His average of runs per match increased by 2. What was his average before the 21st match?

The average weight of 8 people is increased by 2 kg when a new person comes in place of the person who weighs 50 kg. What is the weight of the newcomer?

The average age of three boys is 15 years if their ages are in the ratio 3 : 5 : 7, what will be the age of the youngest boy?