Question

The accompanying data table lists measured voltage amounts supplied directly to a family’s home. The power supply company states that it has a target power supply of 120 volts. Using these home voltage amounts, test the claim that the mean is 120 volts. Use a 0.05 significance level.
Calculate the test statistic.

Answer 1

No one can help if you don't provide all the relevant info.

Answer 2

Day Volts Day Volts
1 124.5 21 124.0
2 123.9 22 123.9
3 123.9 23 123.6
4 123.8 24 124.2
5 123.4 25 123.4
6 123.3 26 123.4
7 123.3 27 123.4
8 123.6 28 123.4
9 123.5 29 123.3
10 124.1 30 124.4
11 123.5 31 123.5
12 123.7 32 123.6
13 124.1 33 123.8
14 123.7 34 123.9
15 123.9 35 123.9
16 124.0 36 123.8
17 124.2 37 123.9
18 123.8 38 123.7
19 123.8 39 123.8
20 123.8 40 123.8

Answer 3

Ugh, this isn't an incredibly user-friendly format... Anyway, the first thing to do is compute the mean of the sample, so take the average of the "Volts" data (see the pic below).

We'll use a \(Z\) test to compare this sample mean to the predicted mean.
\[Z=\frac{123.763-120}{0.295858}\approx12.7\]

Answer 4

If you're at all familiar with the standard normal distribution, the conclusion should be obvious, but if you're not, consult a table of \(z\) scores, like the one linked here:
http://www.rochester.edu/college/psc/clarke/201/ztable2.jpg

Notice that our calculated \(Z\) is not even listed.