Question

The average of 17 numbers is 45. The average of first 9 of those is 51 and the last 9 of those is 36. What is the ninth number

Answer 1

Answer:

Answer will be 18.

Let the sum of first 8 digits be ‘a’.

Let ninth number be ‘b’.

Let sum of last 8 digits be ‘c’.

So from the question, first equation will be:-

(a+b+c)/17 = 45

Second equation will be:-

(a+b)/9 = 51

Third equation will be:-

(b+c)/9 = 36

Solving these 3 liner equation will get the value of ‘b’ as 18, which is the ninth number.