4.20. For 5459 pregnant women using Aarhus Univer- sity Hospital in Denmark in a two-year period who reported information on length of gestation until birth, the mean was 281.9 days, with standard devi- ation 11.4 days. A baby is classified as premature if the gestation time is 258 days or less.

(a) If gestation times are normally distributed, what proportion of babies would be born pre- maturely?