What proportion of women are underweight?

Question

a study suggested that women between ages 20 and 29 in the US have a mean BMI of 26.8 and standard deviation of 7.4
(lets assume these BMIs are normally distributed)

 

a BMI less than 18.5 is considered being underweight

Answer 1

x = 18.5

μ = 26.8

σ = 7.4

 

P(X < x) = P[(X-μ)/σ < (x-μ)/σ]

P(X < 18.5) = P[Z < (18.5 - 26.8)/7.4] = P(Z < -1.12)

From the table of normal distribution for z = -1.12, we get 0.131357.