Question

Fill in the blank. In a drive thru performance study, the average service time for McDonald's is 203.21 seconds with a standard deviation of 5.67 seconds. A random sample of 90 times is taken. There is a 51% chance that the average drive-thru service time is less than ________ seconds.

1)

203.22

2)	There is not enough information to determine this.

3)

203.2

4)

203.07

5)

203.35

Answer 1

Given that,

mean = = 203.21

standard deviation = = 5.67

n = 90

= 203.21

= / n = 5.67/ 90 =0.5977

Using standard normal table,

P(Z < z) = 51%

= P(Z < z) = 0.51

= P(Z <0.025 ) = 0.51

z = 0.025

Using z-score formula  

= z * +

=0.025 *0.5977+203.21

= 203.22