How many plots of corn should be planted?
From previous experience, we expect the yield to be just over 100 bushels per acre with standard deviation about 8.
How many plots should be planted to estimate the mean yield to within 2 bushels per acre with probability 0.95?
The diagram finds the sample size by a trial-and-error method. For any values of n and s, it finds the width of the resulting confidence interval.
Use the bottom slider to set the standard deviation to 8. Then drag the sample size slider and verify that n should be 64 or higher to get the '±' value below 2.
Solving an equation
You could also mention that, provided n is reasonably large (so that the t-value will be approximately 1.96), the equations can be solved to give