Step 1:
We find the mean of the original data set
(10+20+15+30+15) divided by 5
90/5 = 18
Step 2:
We now find the mean of given data set plus the added 6
(10+20+15+30+15+6) divided by 6
96/6 = 16
Step 3:
We then compare the mean in step one (18) and the mean in step two (16)
18 - 16 = 2
Conclusion:
When 6 is added to the given data set, the mean is reduced by 2
