<PRE><B>Question 1159163</B>

Ho: Lifetime is 1400 hours 
Ha: Lifetime is not 1400 hours
alpha=0.05 p{reject Ho|Ho true}
test is t0.975, df=24)
critical value is t&gt;2.064
for 95%CI use mean+/-t*s/sqrt(n)
this is 1580+/-2.064*80/sqrt(25)
half-interval is 33 hours
CI is (1547, 1613)
1400 does not lie in the interval and therefore can assume the mean lifetime is not 1400 hours but rather longer.</PRE>