Studies have determined that the average gestation period (time between conception and giving birth) for humans to be nearly 266 days, while the standard deviation (σ) is about 16 days.  If the length of gestation is considered to follow a normal distribution, then find the percent of pregnancies which would be expected to last:

1.  between 266 days and 280 days?

    

    

    

    

    

    

2.  more than 39 weeks?