Question

In a study of 225 adults, the mean heart rate was 72 beats per minute. Assume the population of heart rates is known to be approximately normal with a standard deviation of 10 beats per minute. What is the 90% confidence interval for the mean beats per minute?

Answer 1

Confidence interval lower bound = 72-1.097 = 70.903

Upper bound = 72+1.097=73.097

Explanation:

In a study of 225 adults, the mean heart rate was 72 beats per minute

Hence sample size n = 225

sigma = population std deviation = 10

Sample std deviation = 10/sqrt 225 = 0.67

Since n is sufficiently large we can use Z critical value for finding confidence interval 90%

Two tailed z critical for 90% is 1.645

Margin of error = 1.645 *0.67=1.097

Confidence interval lower bound = 72-1.097 = 70.903

Upper bound = 72+1.097=73.097

Answer 2

The lower and upper bounds of the confidence intervals must be equally distanced from the mean
so it will be
70.9 - 73.1
hope it helps