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'Dopey Measurement' printed from https://nrich.maths.org/
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