In: Math
The drive-thru times at Tim Horton’s are normally distributed with µ = 138.5 seconds and σ = 29 seconds.
(a) What is the probability that a randomly selected car will get through the drive-thru in less than 100 seconds?
(b) What is the probability that a randomly selected car will spend more than 160 seconds in the drive-thru?
(c) What proportion of cars spend between 2 and 3 minutes in the drive-thru?
(d) Would it be unusual for a car to spend more than 3 minutes in the drive-thru? Why?
According to the given question, the drive-thru times at Tim Horton’s are normally distributed with mean
seconds and standard deviation
seconds.
(a) The probability that
a randomly selected car will get through the drive-thru in less
than 100 seconds is 
.
Explanation:




The area under the standard normal curve 
 is determined from a standard normal table as:

The area is shaded in black as:

(b) The probability that
a randomly selected car will spend more than 160 seconds in the
drive-thru is 
.
Explanation:




The area over the standard normal curve from 
 is determined from a standard normal table as:

The area is shaded in black as:

(c) The proportion
of cars spend between 2 and 3 minutes in the drive-thru
is  
or 66.2 %.
Explanation:




The area under the standard normal curve from 
 and 
 is determined from a standard normal table as:

The area is shaded in black as:

(d) The probability that a car to spend more than 3 minutes in
the drive-thru is 
Explanation:




The area over the standard normal curve from 
 is determined from a standard normal table as:

The area is shaded in black as

As the
probability that a car to spend more than 3 minutes in the
drive-thru is 
 is more than 
, therefore this is not
unusual.
