Question

The lifetime of a particular brand of A batteries follows a normal distribution. The mean lifetime of particular brand of A batteries is 1000 hours, with a standard deviation of 100 hours.

1. What percentage of batteries last more than 1100 hours?
a. 2.5%.
b. 5%.
c. 16%.
d. 32%.
2. What is the probability that a randomly selected battery lasts more than 875 hours?
a. 0.3749.
b. 0.8944.
c. 0.8716.
d. 0.1056.
3. What is the probability that a randomly selected battery lasts between 1150 and 1250 hours?
a. 0.2417.
b. 0.4332.
c. 0.9915.
d. 0.3085.

Answer 1

1. d. 32%

2. a. 0.3749

3. c. 0.9915

Step-by-step explanation:

Percentage of battery is calculated by;

mean - sample / standard deviation

1100 hours - 875 / 100 = 225 / 875 = 0.3749

z-score calculated based on the probability of battery is 0.6549

[ 1250 - 1150 ] / 1250 = 0.9915