Question

a study studied the birth weights of 1,999 babies born in the United States. The mean weight was 3234 grams with a standard deviation of 871 grams. Assume that birth weight data are approximately bell-shaped. Estimate the number of newborns who weighed between 1492 grams and 4976 grams. Write only a number as your answer. Round your answer to the nearest whole number.

Answer 1

1899

Explanation:

The Empirical Rule states that, for a normally distributed random variable:

68% of the measures are within 1 standard deviation of the mean.

95% of the measures are within 2 standard deviation of the mean.

99.7% of the measures are within 3 standard deviations of the mean.

In this problem, we have that:

Mean = 3234

Standard deviation = 871

Percentage of newborns who weighed between 1492 grams and 4976 grams:

1492 = 3234 - 2*871

So 1492 is two standard deviations below the mean.

4976 = 3234 + 2*871

So 4976 is two standard deviations above the mean.

By the Empirical Rule, 95% of newborns weighed between 1492 grams and 4976 grams.

Out of 1999:

0.95*1999 = 1899

So the answer is 1899