A genetics lab wants to alter a species of mosquitoes so that the mean life span becomes shorter. To test whether their effects have been successful, the mean life span of a sample of 40 genetically altered mosquitoes is compared to a sample of 100 unaltered mosquitoes as a control group. The altered mosquitoes had a sample average life span of 17.3 days and a sample standard deviation of 5.4 days. The control group had a sample average life span of 18.8 days with a sample standard deviation of 6.6 days. Assuming that the two groups would have unequal variances, what would be the t-statistic be for the test with the null hypothesis that the means are equal, tested against the alternative hypothesis that the mean for altered mosquitoes is less than the mean of the control group?
-0.668
-1.276
-1.390
-2.213
-3.346