Question

The lengths of one-year-old baby girls can be described using a normal distribution with a mean of 29 inches and a standard deviation of 1.2 inches. using the 68-95-99.7 rule, what percent of one-year-old girls are smaller than 27.8 inches?

Answer 1

The '68-95-99.7 ' rule says,

-About 68% of values fall within one standard deviation of the mean.

-About 95% of the values fall within two standard deviations from the mean.

-Almost all of the values — about 99.7% — fall within three standard deviations from the mean.

Here

`27.8=29-1*1.2`

The length falls within one standard deviation of the mean.

Therefore, the probability
`P(27.8<L<30.2)=0.68`

The required probability is

`P(L<27.8)=(1-0.68)/(2)=0.16`