Answer:
The standard deviation of the sample mean is 16.98.
Step-by-step explanation:
The standard deviation of the sample mean differences is given as by the difference of the 2 standard deviations.This is given as
Difference of standard deviations=21.2-17.6 = 3.6
Now the ratio of the difference to the largest standard difference is given as
Ratio=3.6/21.2=0.1698
Converting this into percentage as 0.1698x100=16.98
The standard deviation of the sample mean is 16.98.