a.
To determine: the fractions of these batteries that should last at least 10 hr.
About
Given information:
A certain brand of AAA batteries lasts an average of 13 hr, with a standard deviation of 1.2 hr. The lifespans can be described by a Normal model.
Concept Used:
z-score:
Calculation:
Using the z-score formula, substitute
Look at the relevant part of the table of z-scores.
Notice, that for
b.
To determine: the probability that a battery will last between 14 and 15 hr.
The probability that a battery will last between 14 and 15 hr is 0.115.
Given information:
A certain brand of AAA batteries lasts an average of 13 hr, with a standard deviation of 1.2 hr. The lifespans can be described by a Normal model.
Concept Used:
z-score:
Calculation:
About
Using the z-score formula, substitute
Use the technology, to determine the probability that a battery will last between 14 hr.
Using the z-score formula, substitute
Use the technology, to determine the probability that a battery will last between 15 hr.
c.
To determine: the guaranteed lifespan that could achieved by at least 96% of them.
The guaranteed lifespan is 10.9 hr.
Given information:
A certain brand of AAA batteries lasts an average of 13 hr, with a standard deviation of 1.2 hr. The lifespans can be described by a Normal model.
Concept Used:
z-score:
Calculation:
From z-table, obtain for 96% probability is
Chapter 10 Solutions
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