In a foundry producing castings, the variance in the mass of a sample of 20 castings taken from a large batch is calculated to be 1.36 kg. Calculate the true variance of the mass for a whole batch of...

In a foundry producing castings, the variance in the mass of a sample of 20 castings

taken from a large batch is calculated to be 1.36 kg. Calculate the true variance of the

mass for a whole batch of castings from which the sample was taken to (a) a 90%