The length of pregnancies of humans has a mean of 265 days and a standard deviation of 10 days.

(a)

What is the value for k for the length of pregnancies in the interval between 250 and 280 days?

At least what percentage of pregnancies is between 250 and 280 days? (Round your answer to one decimal place.)

%

(b)

At least what percentage of pregnancies is between 247.5 and 282.5 days? (Round your answer to one decimal place.)