Researchers are interested in whether the effects of DDT poisoning in rats are less extreme in males. An SRS of 100 male rats and an independent SRS of 100 female rats are obtained. The male rats had a sample mean of 39 and a sample standard deviation of 8. The female rats had a sample mean and standard deviation of 40 and 10, respectively. Let₁represent the true mean response for the males and₂represent the true mean response of the females. They test the following hypotheses:

H₀:₁=₂,H_a:₁<₂

The numerical value of the standard error of the difference in sample means is

choose between these

1.28

1.64

9

3