Using it's formula, it is found that the standard error of the difference of sample means is of 0.443.
The standard error for each sample is given by the sample standard deviation divided by the square root of the sample size, hence:
[tex]s_C = \frac{2.9}{\sqrt{50}} = 0.41[/tex]
[tex]s_A = \frac{1.3}{\sqrt{60}} = 0.168[/tex]
For the distribution of the difference of sample means, the standard error is the square root of the sum of the standard error of each sample squared, hence:
[tex]s = \sqrt{s_C^2 + s_A^2} = \sqrt{0.41^2 + 0.168^2} = 0.443[/tex]
The standard error of the difference of sample means is of 0.443.
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