The length of a human pregnancy is normally distributed with a mean of 272 days with a standard deviation of 9 days (Bhat & Kushtagi, 2006). To find the area under a normal curve we use the normalcdf function in our calculators It is found in the Distr menu. Normalcdf (lower x-value, upper x-value, mean, standard deviation) Using your calculator, calculate probability of a pregnancy that will last between 263 to 281 days? th What is the lower x-value? What is the upper x-value? Can you enter infinity into the calculator? Use 1 x 1099 by entering What is the probability that a pregnancy will last more than 280 days? What if you wanted to use negative infinity in a problem? What is the probability that a pregnancy will last less than 265 days?