Question

It is known that the birth weights of full-term newborn infants in the U.S. have an approximately normal distribution with a mean weight of 6.8 lbs and a standard deviation of 1.7. Approximately what proportion of newborn babies will have a birth weight between 6 lbs and 8 lbs? Provide all four decimal places in your answer.

Answer 1

Answer: 0.4419

Step-by-step explanation:

Given: The birth weights of full-term newborn infants in the U.S. have an approximately normal distribution with a mean weight of 6.8 lbs and a standard deviation of 1.7.

i.e. $\mu=6.8\ \ \ \text{ and }\sigma= 1.7$

Let X denotes the birth weight.

Then, the proportion of newborn babies will have a birth weight between 6 lbs and 8 lbs is given by :-

$P(6<X<8)=P(\dfrac{6-6.8}{1.7}<\dfrac{X-\mu}{\sigma}<\dfrac{8-6.8}{1.7})\\\\=P(-0.47<Z<0.71)\ \ \ [Z=\dfrac{X-\mu}{\sigma}] \\\\=P(Z<0.71)-(1-P(Z-0.47))\\\\=0.7611-(1-0.6808)\ \ \ [\text{By z-table}]\\\\= 0.4419$

Hence, the proportion of newborn babies will have a birth weight between 6 lbs and 8 lbs is 0.4419 .