The following data represent the battery life in hours for

The following data represent the battery life , in hours, for the random sample of ten full charges on ipod music player.

7.3 10.2 12.9 10.8 12.1 6.6 10.2 9.0 8.5 7.1

a) construct a 90% confidence interval for the mean number of hours the battery will last on this player.

(show results in this format x-e <u <x+e if possible)

b) suppose you wanted more accurancy. What can be done to increase the accuracy of the interval without changing the level of confidence? Show an example.

Show work.

Solution

Here,

Xbar = 9.47
s = 2.14064

Thus, the standard error is

sX = s / sqrt(n) = 0.67693

Thus, using TInterval function in ti-84, thr confidence interval is

9.47 - 0.55587 < u < 9.47 + 0.55587 [ANSWER, a]

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We can add more data points. That will lessen the standard error, as it reduces with sqrt(n).