With $N=36$, $\sum fd^2=197500$ and $\sum fd=-750$, the variance of the distribution to three decimal places is:
- 5486.111
- 5052.083
- 4618.056
- 434.028
Show answer and solution
Correct answer: B. 5052.083
1. Use $\sigma^2=\dfrac{\sum fd^2}{N}-\left(\dfrac{\sum fd}{N}\right)^2$.
2. First term: $\dfrac{197500}{36}=5486.111$.
3. Second term: $\left(\dfrac{-750}{36}\right)^2=(-20.8333)^2=434.028$.
4. Subtract: $5486.111-434.028=5052.083$.
5. $5486.111$ stops after step 2; $434.028$ reports only the correction; $4618.056$ subtracts twice.
_Source: NECTA ACSEE 2023 Advanced Mathematics 142/1, Question 4: Statistics_