Question

Your body mass index (BMI) is your weight in kilograms divided by the square of your height in meters. High BMI is a common but controversial indicator of overweight or obesity. A study by the National Center for Health Statistics found that the BMI of American young men (ages 20-29) is approximately Normal with mean 25.8 and standard deviation 4.2. To have a BMI higher than 90% of all men aged 20-29, what would your BMI would need to be?

Answer 1

Given that,

mean = = 25.8

standard deviation = =4.2

Using standard normal table,

P(Z > z) = 90%

= 1 - P(Z < z) = 0.90

= P(Z < z ) = 1 - 0.90

= P(Z < z ) = 0.1

= P(Z < z ) = 0.1

z = -1.28 (using standard normal (Z) table )

Using z-score formula  

x = z * +

x=-1.28 *4.2+25.8

x= 20.424