The life in hours of a certain
The life in hours of a certain type of lightbulb is normallydistributed with a known standard deviation of 10 hours. A randomsample of 15 lightbulbs has a sample mean life of 1000 hours. Whatwould the 99% lower-confidence bound L on the mean life be, roundedto the nearest integer?
Answer:
Solution :
Given that,
= 1000
s = 10
n = 15
Degrees of freedom = df = n – 1 = V – 1 = 14
At 99% confidence level the t is ,
= 1 – 99% = 1 – 0.99 = 0.01
/ 2 = 0.01 / 2 = 0.005
t/2,df = t0.005,14 = 2.977
Margin of error = E = t/2,df* (s /
= 2.977 * (10 /
= 7.686
Margin of error = 7.686
The 99% confidence interval estimate of the population meanis,
– E < 
< + E
1000 – 7.686 < < 1000 + 7.686
992.314 < < 1007.686
(992.314, 1007.686 )
"Our Prices Start at $11.99. As Our First Client, Use Coupon Code GET15 to claim 15% Discount This Month!!"
