For 36 stones with assumed mean $A=225$, $\sum fd=-750$ and $\sum fd^2=197500$, the mean by the deviation method to three decimal places is:

1. The deviation-method mean is $\bar{x}=A+\dfrac{\sum fd}{N}$. 2. Substitute $A=225$, $\sum fd=-750$ and $N=36$. 3. $\dfrac{-750}{36}=-20.8333\ldots$ 4. So $\bar{x}=225-20.833=204.167$ to three decimal places. 5. $225$ ignores the correction term; $245.833$ adds instead of subtracting; $204.170$ rounds to three decimals too early. _Source: NECTA ACSEE 2023 Advanced Mathematics 142/1, Question 4: Statistics_