Sum of first n natural numbers

Q. Arithmetic mean of the numbers 12, 24, 56, 74 and 32 = ______

1. 40
2. 39.8
3. 39.6
4. 40.2

Q. Consider the following AP:
24, 21, 18.....
How many terms of this AP must be taken so that their sum is 78?

Q. Arithmetic mean of 2, 5, 8, ... upto 13 terms = ______

1. 10
2. 12
3. 16
4. 20

Q. Write any two demerits of arithmetic mean with its definition

Q.

If $a_1,a_2,....a_n$ are positive numbers such that $a_1·a_2·a_3·....·a_n=1$, then their sum is:

1. A positive integer.

2. Divisible by $n$.

3. Never less than $n$.

4. None of these.

Q. Arithmetic mean of the numbers 12, 24, 56, 74 and 32 = ______

1. 40
2. 39.8
3. 39.6
4. 40.2

Q. Arithmetic mean for the given data is

Marks	No. of students
0-10	5
10-20	10
20-30	25
30-40	30
40-50	20
50-60	10

1. $35$
2. $34$
3. $33$
4. $38$