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.

The mean weight of 60 students of a class is 52.75 kg. If the mean weight of 25 of them is 51 kg, find the mean weight of the remaining students.

The mean of five numbers is 18. On excluding one number, the mean becomes 16. Find the excluded number.