Question

Twelve-year-olds have heights that are normally distributed with a mean of heights of 57 inches and a standard deviation of 4.6 inches. what percent of 12-year-old boys will have heights less than 55 inches?

A) 33%
B) 37%
C) 42%
D) 49%

Answer 1

A

Explanation:

To calculate this, the first thing we need to do is to calculate the z-score

Mathematically,

z-score =( x - mean )/SD

according to the question, X = 55 inches, mean = 57 inches and SD = 4.6 inches

we plug these values into the equation

z-score =( 55-57)/4.6 = -2/4.6 = -0.4348

The required probability we are trying to calculate is;

P( z < -0.4348) or simply P(x<55)

To calculate this probability we use the standard score table

From the standard score table,

P( z < -0.4348) = 0.33186

In percentage this is 33.186%

To the nearest percentage, this is 33%