SOLUTION: If anyone can help me with these questions I would greatly appreciate it as I am having problems with them &showing my work for them. Thank you. 1. Find the critical value zc ne

Question 482293: If anyone can help me with these questions I would greatly appreciate it as I am having problems with them &showing my work for them. Thank you.
1. Find the critical value zc necessary to form a confidence interval at the given level of confidence. (References: definition for level of confidence page 311, end of section exercises 5 � 8 page 317) (2.5 points each)
a. 90%

b. 80%

2. The new Twinkle bulb has a standard deviation of 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be 550 hours.
a. What is the margin of error [E] for a 90% confidence interval? Round your answer to the nearest hundredths (5 points)
(References: definition of margin of error on page 312 and example 2 on page 312).

b. Construct a 90% confidence interval for the mean life of all Twinkle bulbs.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
1. Find the critical value zc necessary to form a confidence interval at the given level of confidence. (References: definition for level of confidence page 311, end of section exercises 5 � 8 page 317) (2.5 points each)
a. 90%
Find the z-value with a right tail of 5%:
Ans: z = 1.645
=====================
b. 80%
Find the z-value with a right tail of 10%:
Ans: 1.2816
==============================

2. The new Twinkle bulb has a standard deviation of 35 hours. A random sample of 50 light bulbs is selected from inventory. The sample mean was found to be
550 hours.

a. What is the margin of error [E] for a 90% confidence interval? Round your answer to the nearest hundredths (5 points)
ME = 1.645 = 8.14
---------
(References: definition of margin of error on page 312 and example 2 on page 312).

b. Construct a 90% confidence interval for the mean life of all Twinkle bulbs.
x-bar = 550
ME = 1.9126
-----
90% CI: 550-8.14 < u < 550+8.14
541.86 < u < 558.14
============================
Cheers,
Stan H.
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