Question

LifeCharge Batteries claims that their batteries last an average of 210 hours when used in a hand held gaming system, with a standard deviation of about 9 hours. An independent quality control company took a sample of 34 batteries, and used the same hand held gaming system that LifeCharge used to record the time the batteries lasted.

1. Assuming the claim is true, what is the probability that the value of the sample mean is greater than 251.7 hours.
2. The sample mean was found to be 251.7, what does this say about the claim?
A. The sample mean is quite far off from the mean claimed, casting doubt on the current mean.
B. The sample mean is sufficiently close to the mean claimed, supporting the current mean.
C. The sample mean found does not truly support nor cast doubt on the current mean.

Answer 1

The answer is "0.0023 and Choice a"

Explanation:

In point a:

The central limit theorem:

`\mu_(X)= 250\\\\\sigma_(X)=(\sigma)/(√(n))=(6)/(√(100)) =0.6\\\\P(\bar{X}>251.7)\\\\=P(z>(251.70-250)/(0.6))\\\\=P(z>2.83)\\\\=1-0.9977\\\\=0.0023`

In point b:

The chance is lower than 0.05. This means that it is very rare to see the average sample above 251.8 if the argument is valid, that is why the means of the sample is far away from the common claimed and casts doubt on the actual mean.