A psychologist claims that the mean age at which children start walking is 12.5 months. The average age 20 randomly selected children starting walking was at 13.6 months with a standard deviation of 1.85.

a. What is the point estimate? Be sure to use the correct symbol.

b. A 90% confidence interval is to be computed. What is the critical value you will use?

c. What is the standard error?

d. What is the margin of error?