The breaking strengths for 1-foot-square samples of a particular synthetic fabric are approximately normally distributed with a mean of 2,250 pounds per square inch (psi) and a standard deviation of 10.2 psi. Find the probability of selecting a 1-foot-square sample of material at random that on testing would have a breaking strength in excess of 2,265 psi.

• Refer to above exercise. Suppose that the mean breaking strength for the sample of 15 1-foot sections of the new synthetic fabric is 2,268 psi. What is the probability of observing a value of equal to or greater than 2,268, assuming that the mean breaking strength for the new fabric is 2,250, the same as that for the old?

Can you help me solve this? and tell me where all numbers come from. Thank you!