Question 868431
Use <a href="http://3.bp.blogspot.com/_5u1UHojRiJk/TEdJJc6of2I/AAAAAAAAAIE/Ai0MW5VgIhg/s1600/t-table.jpg">a table</a> to find that the critical value is {{{t=2.821}}}. The degrees of freedom are {{{df = n-1 = 10-1 = 9}}}. Look in the row that starts with {{{9}}} and look above the 98%. The value you'll see in this spot is {{{2.821}}}



So we're given



xbar = 1200 (sample mean)
t = 2.821 (see above)
s = 100 (sample standard deviation)
n = 10 (sample size)



Now compute the lower bound (L) and the upper bound (U) of the confidence interval.



Lower Bound:


L = xbar - t*s/sqrt(n)
L = 1200 - 2.821*100/sqrt(10)
L = 1,110.79214720666



Upper Bound:


U = xbar + t*s/sqrt(n)
U = 1200 + 2.821*100/sqrt(10)
U = 1,289.20785279334



The 98% confidence interval is approximately <font color="red">(1110.79214720666,   1289.20785279334)</font>



So if we construct 100 confidence intervals, then about 98 of them will contain the true population mean.