Suppose that the weight of male babies less than 2 months old is normally distributed with mean 11.5 pounds and standard deviation 2.7 pounds. A sample of 36 babies is selected. What is the probability that the average weight of the samlpe is less than 11.29 pounds?

Answer 1

Use z-scores and a z-table for this problem. Because you are given a sample size, you will need to include the sample size in the calculation:

z = (x - mean)/(sd/√n)

Your data:
z = (11.29 - 11.5)/(2.7/√36)

Finish the calculation. Use the z-table to find the probability (remember that the problem is asking "less than 11.29" when looking at the table).

I hope this will help get you started.