Average Discovery
Find the missing number if the mean, median and mode are all the same.
Age
14 to 16
Challenge level
Problem
The mean, median and mode of five numbers are all the same.
If four of the numbers are 7, 7, 5 and 7, what is the fifth number?
Student Solutions
Whatever the missing number is, the median and mode will still be 7.
For the mean to be 7, the total must be 35.
So the missing number is 9.