Concept explainers
a.
To calculate: The percent of light bulbs that will last for less than 900 hours.
a.
Answer to Problem 7WE
The percent of light bulbs that will last for less than 900 hoursis
Explanation of Solution
Given information:
900 hours is the mean life of a certain kind of light bulb with a standard deviation of 30 hours.
Formula used:
The number x is known as standardized value to z where z is provided value of
Calculation:
Consider the provided information that 900 hours is the mean life of a certain kind of light bulb with a standard deviation of 30 hours.
To compute percent of light bulbs that will last for less than 900 hours.
Recall that the number x is known as standardized value to z where z is provided value of normal distribution, m is the mean and
Here, z is 900, m is 900 and
Apply it,
The total area under the curve is 1 and standard normal curve is symmetric about y -axis.
The required percent is the area under the curve of standard normal to the left of
Multiply the result by 100, to obtain the answer in percentage form,
Thus, the percent of light bulbs that will last for less than 900 hours is
b.
To calculate: The percent of light bulbs that will last for more than 984 hours.
b.
Answer to Problem 7WE
The percent of light bulbs that will last for more than 984 hoursis
Explanation of Solution
Given information:
900 hours is the mean life of a certain kind of light bulb with a standard deviation of 30 hours.
Formula used:
The number x is known as standardized value to z where z is provided value of normal distribution, m is the mean and
Calculation:
Consider the provided information that 900 hours is the mean life of a certain kind of light bulb with a standard deviation of 30 hours.
To compute percent of light bulbs that will last for more than 984 hours.
Recall that the number x is known as standardized value to z where z is provided value of normal distribution, m is the mean and
Here, z is 984, m is 900 and
Apply it,
The total area under the curve is 1 and standard normal curve is symmetric about y -axis.
The required percent is the area under the curve of standard normal to the right of
Multiply the result by 100, to obtain the answer in percentage form,
Thus, the percent of light bulbs that will last for more than 984 hours is
Chapter 15 Solutions
Algebra and Trigonometry: Structure and Method, Book 2
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