The average of seven numbers is 18. If one of the numbers is 17 and if it is replaced by 31, then the average becomes :

Answer: Option C

According to the question,
Actual number = 17
New number = 31
Difference = 31 - 17 = 14
Difference '14' effects the seven numbers = $$\frac{14}{7}$$ = 2
∵ Present average = 18
∴ New average = 18 + 2 = 20