The mean life of a particular brand of light bulb is 1200 hours. if you know that at about 95% of this brand of bulbs will last between 1100 and 1300 hours, then what is the standard deviation of the light bulbs’ life?

a) 200
b) 100
c) 50
d) 25
e) 75

c) 50

Step-by-step explanation:

We have been given that the mean life of a particular brand of light bulb is 1200 hours. About 95% of this brand of bulbs will last between 1100 and 1300 hours.

We will use z-score formula to solve our given problem.

, where,

,

,

,

We know that 95% of data points lies within two standard deviation of mean, so 1100 will correspond to a z-score of -2 and 1300 will correspond to a z-score of 2.

We can use sample score 1300 and get same answer as:

Therefore, the standard deviation of the light bulbs’ life is 50 years.

the formula of a slope:

from a table we have

substitute:

the slope of f(x) is -1.

the graph of funcfion g(x) is a horizontal line. the slope of a horizontal line is equal 0. therefore the slope of g(x) is 0.

-1 < 0