QUESTION 17 Lena finds that, in a sample of 36 children, the mean age at which they first begin to combine words is 20.7 months, with a standard deviation of 1.95 months. Identify the correct critical value that you would use to find a 95% confidence interval. O z = 1.960 O t= 2.030 O t= 2.028 QUESTION 18 Lena finds that, in a sample of 36 children, the mean age at which they first begin to combine words is 20.7 months, with a standard deviation of 1.95 months. Identify the correct formula to use to find the margin of error for this problem. O OF = O ST = S OE = Z . OX OE = t . Sx