Standard deviation

Question

A study studied the birth weights of 531 babies born in the United States. The mean weight was 3234 grams with a standard deviation of 871 grams. Assume that the birth data are approximately bell shaped. Estmate the number of newborns who weighed between 1492 grams amd 4976 grams

Answer 1

z₁₄₉₂ = (1492 - 3234) / 871

z₁₄₉₂ = -1742 / 871

z₁₄₉₂ = -2

 

z₄₉₇₆ = (4976 - 3234) / 871

z₄₉₄₆ = 1742 / 871

z₄₉₄₆ = 2

 

What percent of the population is between -2 standard deviations and +2 standard deviations?