# If the Last Number is 20 Then the First Number is:

Out of four numbers the average of the first three is 16 and that of the last three is 15. If the last number is 20 then the first number is:

- 23
- 28
- 25
- 21

**Answer: (1) 23**

**Explanation:-
**The average of first three numbers = 16.

Then, the sum of first three numbers = 16 x 3 = 48

The average of last three numbers = 15

Then, the sum of last three numbers = 15 x 3 = 45

The last number is 20 ,

Then, sum of two number before last number = 45 – 20

= 25

Then, the first number = 48 – 25

= 23

Hence, the answer is (1) 23.