2-2 The Normal Distribution: Activity APPLICATION 2. LENGTHS OF PREGNANCIES 19. The length of human pregnancies from conception to birth varies according to a distribu- tion that is approximately normal, and according to a 2006 paper, "A re-look at the dura- tion of human pregnancy" (Bhat & Kushtagi, Dec. 2006, Singapore Medical Journal, 47(12) 1044-8), pregnancy lengths have a mean of 272 days and standard deviation of 9 days. a. Find the proportion of pregnancies that last more than 280 days. (Hint: Draw a picture of the normal distribution, and mark the days you are interested in.) b. Find the proportion of pregnancies that last between 250 and 280 days. (Hint: Draw picture of the normal distribution, and mark the days you are interested in.)