Jon S. answered • 04/22/20

Patient and Knowledgeable Math and English Tutor

Compute the mean and standard deviation of your sample.

The critical t-value for a 90% confidence it the t-value for sample size - 1 degrees of freedom and 0.05 tail value.

The confidence interval is mean +/- critical t-value * standard deviation/square root(sample size).

If the resultant interval only contains values that are less than 12, then the machine is under filling the cups.