Confidence Intervals?

Question

I cannot do this question, can someone help me as a just get a silly answer?

The average weekly overtime earnings from a sample of workers last year and this year are:
N workers: 15 and 12
Mean overtime earnings: £3.50 and £4
Standard deviation: £2.95 and £3.05

Construct a 95% confidence interval for the increase in average weekly overtime earnings (assume equal standard deviations)

Thanks

So what answer do you get, so I can check mine?

Answer 1

you would need to look at table for t values.
you are looking for a 95% confidence level, so you would divide .5 (which is 1-.95) by 2 and get .025 that is the column you find the value for t.
your n number, the row for the t number, is 15-1 or 14 and 12-1 or 11.
Look at the table IV in colum t=0,025 and row 14 write down the number. that number is the t value for the first equation.
Look at table IV in column t=0.025 and row 11, that is your t value for the second equation.
Now that you have the t values you can plug them into the formula for confidence interval.

Good luck