2d) The difference in the mean length is 18 mm.

The standard deviation for both types of rats ( +/- 5.2 mm & +/- 7.1 mm) is smaller than the difference in the mean length between the 2 populations of rats.

The hypothesis that Vancouver Island rats are longer than those from the mainland coast is supported.

They are larger than the mainland coastal population and the standard deviation of each population is smaller than the difference in their sizes!