16. The average of 25 results is 18; that of first twelve is 14 and of last twelve is 17. Thirteenth result is :

17. The average age of 30 students in a class is 12 years. The average age of a group of 5 of the students is 10 years and that of another group of 5 of them is 14 years. The average age of the remaining students is :

18. If a, b, c, d, e are five consecutive odd numbers, their average is :