How many commuters must be randomly selected to estimate the mean driving time of Chicago commuters? We want 90% confidence that the sample mean is within 4 minutes of the population mean, and the population standard deviation is known to be 12 minutes.

The number of commuters to be randomly selected to estimate the mean driving time of Chicago commuters is 25

Step-by-step explanation:

At  90% confidence

we have

Minimum sample size, n given by

Where:

c = Confidence level = 90%

σ = Standard deviation = 12 minutes

E = Maximum error in estimate = minutes

- = 1.64 and = 1.64

Therefore, = 0.51994 and therefore, n is given by

= 24.2064

As we are talking of population, we round to the next whole number, thus;

n = 25 commuters.

answer: 1 + 1 = 11

step-by-step explanation: