Question

Assume that blood pressure readings are normally distributed with a mean of 117 and a standard deviation of 9.6. If 144 people are randomly selected, find the probability that their mean blood pressure will be less than 119.

Answer 1

0.9938

Explanation:

Let mean blood pressure be = x

Pr ( x < 119 ) can be found using ' z value ' = ( x - u ) ÷ ( s / √n ) ; where x = 119 , u = mean = 117 , n = no. of sample items = 144 , s = standard deviation = 9.6

z = (119 - 117) ÷ (9.6 / 144) = -2 ÷ (9.6 / 12) = -2 / 0.8 → z = 2.5

Pr (x < 119) = P (z < 2.5)

P = 0.9938