<Dd> 9 and − 9 cancel, </Dd> <Dd> 7 + 4 cancels − 6 − 5, </Dd> <P> and so on . We are left with a sum of − 30 . The average of these 15 deviations from the assumed mean is therefore − 30 / 15 = − 2 . Therefore, that is what we need to add to the assumed mean to get the correct mean: </P> <Dl> <Dd> correct mean = 240 − 2 = 238 . </Dd> </Dl>

How to calculate assumed mean in step deviation method