The birth weights for two groups of babies were compared in astudy. In one group the mothers took a zinc supplement duringpregnancy. In another group, the mothers took a placebo. A sampleof 129 babies in the zinc group had a mean birth weight of 3469grams. A sample of 142 babies in the placebo group had a mean birthweight of 3318 grams. Assume that the population standard deviationfor the zinc group is 843 grams, while the population standarddeviation for the placebo group is 775 grams. Determine the 95%confidence interval for the true difference between the mean birthweights for \"zinc\" babies versus \"placebo\" babies.
Step 1 of 2 : Find the critical value that should be used inconstructing the confidence interval.
