Find the mean of each of the following sets of numbers :

(i) 10, 4, 6, 12, 9

(ii) 0.2, 0.02, 2, 2.02, 1.22, 1.02

Find the arithmetic mean of :

(i) first eight natural numbers;

(ii) first five prime numbers;

(iii) first six positive even integers;

(iv) first five positive integral multiples of 3;

(v) all factors of 20.

The marks obtained by 10 students in a class-test were as follows :

38, 41, 36, 31, 45, 38, 27, 32, 29, 39

Find :

(i) the mean of their marks;

(ii) the mean of their marks, when the marks of each student are increased by 2;

(iii) the mean of their marks, when 1 mark is deducted from the marks of each student;

(iv) the mean of their marks, when the marks of each student are halved.

If the mean of 11, 8, 13, 10, x and 9 is 9.5, find the value of x.