Measuring Intelligence in Children Mental measurements of young children are often made by giving them blocks and telling them to build a tower as tall as possible.

One experiment of block building was repeated a month later, with the times (in seconds) listed in the accompanying table (Based on data from “Tower Building,” by Johnson and Courtney, Child Development, Vol. 3).

a. Is there sufficient evidence to support the claim that there is a difference between the two times? Use a 0.01 significance level.

b. Construct a 99% confidence interval for the mean of the differences. Do the confidence interval limits contain 0, indicating that there is not a significant difference between the times of the first and second trials?

Child A B C D E F G H I J K L M N O First trial 30 19 19 23 29 178 42 20 12 39 14 81 17 31 52 Second trial 30 6 14 8 14 52 14 22 17 8 11 30 14 17 15