Question

The average amount of milligrams (mg) of sodium in the water in a certain neighbourhood in Winnipeg is 60 mg/l, and the standard deviation is 10 mg/l. Assume the variable is normally distributed.

(a) If a sample of water is selected form the neighbourhood, what is the probability that the sodium content will be more than 70 mg/l?
(b) If 10 samples of the water from the neighbourhood is selected, what is the probability that the mean of the sample will be larger than 70 mg/l?
(c) Why is the probability for part (a) greater than that for part (b)?

Answer 1