The time required for an automotive center to complete an oil change service on an automobile approximately follows a normal​ distribution, with a mean of 19 minutes and a standard deviation of 3.5 minutes. ​(a) The automotive center guarantees customers that the service will take no longer than 20 minutes. If it does take​ longer, the customer will receive the service for​ half-price. What percent of customers receive the service for​ half-price? ​(b) If the automotive center does not want to give the discount to more than 2​% of its​ customers, how long should it make the guaranteed time​ limit?

Respuesta :

Answer:

a. 61.41%

b. 27 minutes

Step-by-step explanation:

a:  Find the z-score for the situation.  

µ = 19

x-bar = 20

σ = 3.5

  z = (20 - 19)/3.5 = 0.29

The p-value for z = 0.29 is 0.6141, so 61.41% of people will get this discount

b:  They want no more than 2% to get the discount, so they want less than 98% getting the discount.  The z-score for 98% (0.98 as a decimal) is 2.055

*You need to look at the chart and find where 0.98 would be.  It's between a z-score of 2.05 and 2.06.  

The z-score is    2.055 = (x - 19)/3.5      We are solving for the time for this one.  So solve for x...

              7.1925 = x - 19      (multiply both sides by 3.5)

             26.1925 = x    (add 19 to both sides)

So 26.1925 minutes, or about 26 minutes, 12 seconds, so round up to 27 minutes because they want less than 2%.   I chose 27 minutes because no places give odd wait times like 26 minutes 12 seconds.

       

A) The percent of customers receive the service for​ half-price is; 61.41%

B) The time to make the guaranteed limit is; 26 minutes 12 seconds

What is the p-value of the distribution?

A) We are given;

Population mean; µ = 19

Sample mean; x' = 20

Standard deviation; σ = 3.5

Thus, z-score is;

z = (20 - 19)/3.5

z = 0.29

From online p-value from s-score calculator,  the p-value for z = 0.29 is;

p = 0.6141 = 61.41%

B) We are told that they now want more than 2% to get the discount. This means that they want less than 98% or 0.98 getting the discount.  

The z-score for 0.98 is; z = 2.055

Thus, using z-score formula, we have;

2.055 = (x' - 19)/3.5    

x' - 19 = 3.5 * 2.055

x' - 19 = 7.1925

x' = 26.1925 = 26 minutes 12 seconds

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