in a sample of 80 children, the mean age at which they first begin to combine words is 16.48 months, with a standard deviation of 8.58 months. construct a 98% confidence interval for the mean age at...

in a sample of 80 children, the mean age at which they first begin to combine words is 16.48 months, with a standard deviation of 8.58 months. construct a 98% confidence interval for the mean age at which children in the population first begins to combine words.