The mean age of eight boys is 16 years. If two more boys, with ages 18 years and 14 years, join them, the resulting mean age is :

1. 18 years

2. 14 years

3. 16 years

4. 32 years

The mean value of 15 numbers is 20. If one of these numbers is wrongly taken as 45 instead of 15, the correct mean is :

1. 30

2. 15

3. 20

4. 18

Marks obtained (in mathematics) by 9 students are given below :

60, 67, 52, 76, 50, 51, 74, 45 and 56.

(a) Find the arithmetic mean.

(b) If marks of each student be increased by 4; what will be the new value of arithmetic mean?

(a) Find the mean of 7, 11, 6, 5 and 6.

(b) If each number given in (a) is diminished by 2; find the new value of mean.