Olivia works at a company that creates mobile phones. She wanted to estimate the mean amount of time their new phone's battery lasts with regular use after a full charge. She took a random sample of 6
66 of these phones and randomly assigned each of them to a volunteer. She instructed them to fully charge the phones and use them as they regularly would until the battery died (without recharging the phone). Here are the data they reported:
Phone
1
11
2
22
3
33
4
44
5
55
6
66
Battery life (hours)
8.0
8.08, point, 0
6.0
6.06, point, 0
10.5
10.510, point, 5
9.0
9.09, point, 0
8.5
8.58, point, 5
12
1212
Mean
x
ˉ
=
9
x
ˉ
=9x, with, \bar, on top, equals, 9 hours
Standard deviation
s
x
=
2.07
s
x
​
=2.07s, start subscript, x, end subscript, equals, 2, point, 07 hours
Assume that all conditions for inference are met.
Which of the following is a
90
%
90%90, percent confidence interval for the mean battery life (in hours)?
Choose 1
Choose 1

(Choice A)
A
9
±
1.4
9±1.49, plus minus, 1, point, 4

(Choice B)
B
9
±
1.7
9±1.79, plus minus, 1, point, 7

(Choice C)
C
9
±
2.0
9±2.09, plus minus, 2, point, 0

(Choice D)
D
9
±
2.07
9±2.079, plus minus, 2, point, 07