Question

A.) Response times were recorded for 40 randomly selected customers of phone company A answering a phone call. Those times had a mean of 23.95 seconds and a standard deviation of 2.55 seconds. Construct a 99% C.I. estimate of the population mean.

B.) Response times were recorded for 35 randomly selected customers of phone company B answering a phone call. Those times had a mean of 18.95 seconds and a standard deviation of 1.30 seconds. Construct a 99% C.I. estimate of the population mean.

C.) Use parts A) and B) to determine if Phone Company or Phone A, Company B is more efficient. Explain.

(Please show all work and label if its a, b, or c.)

Answer 1

Answer:

a)

Given,

sample n = 40

xbar = 23.95

standard deviation = 2.55

degree of freedom = n - 1

= 40 - 1

= 39

Here at 99% CI, t(alpha/2,df) = t(0.005 , 39) = 2.71

CI = xbar +/- z*s/sqrt(n)

substitute values

= 23.95 +/- 2.71*2.55/sqrt(40)

= (22.857 , 25.043)

b)

sample n = 35

t(alpha/2,df) = t(0.005 , 34) = 2.73

CI = xbar +/- z*s/sqrt(n)

substitute values

= 18.95 +/- 2.73*1.3/sqrt(35)

= (18.35 , 19.55)

c)

Here we observe & say that phone B has the smaller CI, so B is efficient.

answered by: anonymous