Question

The heart rates (in beats per minute) of 41 randomly selected finishers of the Chicago Marathon, five minutes after they completed the race, had sample mean x = 132 and sample variance s2 = 105. Assuming that the heart rates of all finishers of the Chicago Marathon five minutes after completing the race are normally distributed, obtain a 95% confidence interval for their mean.

Answer 1

The 95% confidence interval for the mean heart rate of Chicago Marathon finishers five minutes after completing the race is (128.74, 135.26) beats per minute for variance.

To find the 95% confidence interval for the mean heart rate of Chicago Marathon finishers five minutes after completing the race, we can use the following formula:


`CI = x +- (t * (s / √(n) ))`

where:
- CI is the confidence interval
- x is the sample mean (132)
- t is the t-value corresponding to the 95% confidence level
- s is the square root of the sample variance (the sample standard deviation)
- n is the sample size (41)

Step 1: Calculate the sample standard deviation

`s = √(s^2) = √(105)`≈ 10.25

Step 2: Find the t-value for a 95% confidence level with 40 degrees of freedom (n - 1)
Using a t-table or calculator, we find that the t-value is approximately 2.021.

Step 3: Calculate the margin of error
Margin of Error =
`t * (s / √(n) ) = 2.021 * (10.25 / √(4) )` ≈ 3.26

Step 4: Calculate the confidence interval
CI = x ± Margin of Error = 132 ± 3.26
CI = (128.74, 135.26)

So, the 95% confidence interval for the mean heart rate of Chicago Marathon finishers five minutes after completing the race is (128.74, 135.26) beats per minute.