**Average Aptitude Set 7**

**31) Find the average of first 20 consecutive natural numbers.**

- 12.20
- 10.78
- 16.45
- 10.5

**Answer:** D

**Explanation:**

The average of first n consecutive natural numbers is given by;

=(n+1)/2

Here, n=20

So, average = (20+1)/2

=210/20

=21/2

=10.5

**32) Find the average of square of first 5 consecutive natural numbers.**

- 12
- 10
- 16
- 11

**Answer:** D

**Explanation:**

The average of square of first n consecutive natural numbers is given by;

= (n+1) (2n+1) / 6

Here, n=5

= (5+1) (2*5+1)/6

= 6*11/6

= 11

33) Find the average of cubes of first 7 consecutive natural numbers.

- 112
- 110
- 116
- 113

**Answer:** A

**Explanation:**

The average of cubes of first n consecutive natural numbers is given by;

= n (n+1)²/4

Here, n=7

= 7 (7+1)²/4

= 7*64/4

=448/4

= 112

**34) Find the average of first 8 consecutive odd numbers.**

- 11
- 10
- 8
- 12

**Answer:** C

**Explanation:**

The average of first n consecutive odd numbers is equal to n, so the average of first 8 consecutive odd numbers is 8.

You can check by solving it as show below:

= (1+ 3+ 5+ 7+ 9+ 11+ 13+ 15)/8

= 64/8 = 8

**35) Find the average of the square of first 5 consecutive odd numbers starting from 1 to 9, where the last odd number is 9.**

- 22
- 11
- 16
- 33

**Answer:** D

**Explanation:**

The average of square of first n consecutive odd numbers starting from 1 to X, where the last odd number is X, is given by:

=X(X+2)/3

Here, X=9

So, average =9(9+2)/3

=9*11/3

=99/3

=33

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