Here is one formula for effect size:
Cohen’s d = the difference between two means divided by a standard deviation.
I'll let you take it from here.
a company decides to add a new program that prepares randomly selected sales personnel to increase their number of sales per month. The mean number of sales per month for the overall popualtion of sales people at this national company is 25 with a standard deviation of 4. The mean number of sales per month for those who participated in the new program was 29. Compute the effect size of the new sales program
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