. Does playing memory games improve recall speed in dementia patients? A study designed to investigate this question measured the recall speed of a random sample of 56 dementia patients before and after one month of playing memory games daily. The differences in the recall speeds (before – after) have a mean of 2.813 seconds and a standard deviation of 1.245 seconds. Construct and interpret a 90% confidence interval for the mean difference in recall speeds for all dementia patients who play one month of memory games daily.