A random sample of 500 fish is taken from a lake and marked. After a suitable interval a second sample of 500 is taken and 25 of these are found to be marked. By considering the second sample estimate...

A random sample of 500 fish is taken from a lake and marked. After a suitable interval a second sample of 500 is taken and 25 of these are found to be marked. By considering the second sample estimate the number of fish in the lake.

The standard deviation for a method of measuring the concentration of nitrate ions in water is known to be 0.05 ppm. If 100 measurements give a mean of 1.13 ppm, calculate the 90% confidence limits for the true mean.