Dopey Measurement
How does Snow White need to change her result after the mix-up?
Age
14 to 16
Challenge level
Problem
Snow White wanted to know the mean height of the Seven Dwarfs, so one day she measured them all as they left for work.
She calculated their mean height as 112.3 cm.
Doc complained that she had left him out and measured Dopey twice without him noticing.
If Doc is 3.5 cm taller than Dopey, what is the mean height of the Seven Dwarfs?
Student Solutions
In order to calculate the mean height, Snow White had to first calculate the sum of the heights of the Dwarves.
She calculated their mean height as 112.3 cm, so their heights must have added up to
7 $\times$ 112.3 = 786.1
Since Doc is 3.5 cm taller than Dopey, their heights really add up to
786.1 $+$ 3.5 = 789.6
Therefore the mean height of the Seven Dwarfs is
789.6 $\div$ 7 = 112.8