Question

Assuming an approximately normal data set, find the 99.7% confidence interval for systolic blood pressure in women given a sample size of 1000 with a mean of 123.4 and a standard deviation of 19.9. 

1.73.65 – 173.15 3.103.5 – 143.3
2.63.7 – 183.1 4.83.6 – 163.2

Answer 1

The correct answer is Choice 2: 63.7 to 183.1

A 99.7% confidence interval translates to the area within 3 standard deviations of the mean. We know the standard deviation is 19.9. Now, just multiply that by 3 and you have 59.7.

Add and subtract that from the mean to find the interval.

123.4 + 59.7 = 183.1
123.4 - 59.7 = 63.7