The operators think that machine B tends to deliver a somewhat greater amount than machine A, no matter what the ambient temperature. This is being investigated by an experiment. A random sample of 10 results from the experiment is shown below. Each column of data is for a different ambient temperature

Use an appropriate t test to examine, at the 5% level of significance, whether the mean amount

delivered by machine B may be taken as being greater than that delivered by machine A,

stating carefully your null and alternative hypotheses and the required distributional

assumption.

this is the table

Amount

delivered by 246.2 251.6 252.0 246.6 258.4 251.0 247.5 247.1 248.1 253.4

machine A

Amount

delivered by 248.3 252.6 252.8 247.2 258.8 250.0 247.2 247.9 249.0 254.5

the difference mean is 0.64

but whati don't understandis how they get for the standard deviation s(n-1)=0.8316