Final answer:
The estimated standard error for the sample mean difference is 4.
Step-by-step explanation:
The estimated standard error for the sample mean difference can be calculated using the formula:
SE = √[(s1^2)/n1 + (s2^2)/n2]
where s1 and s2 are the standard deviations of the two samples and n1 and n2 are the sample sizes.
In this case, the two samples have the same size (n = 5) and the pooled variance is 40, which represents the average of the variances of the two samples. Therefore, the estimated standard error for the sample mean difference is:
SE = √[(40/5 + 40/5)] = √[8 + 8] = 4.