The activity of a certain enzyme is measured by counting emissions from a radioactively labeled molecule. For a given tissue specimen, the counts in consecutive 10-second time periods may be regarded (approximately) as repeated independent observations from a normal distribution. Suppose the mean 10-second count for a certain tissue specimen is 1,200 and the standard deviation is 35. Let Y denote the count in a randomly chosen 10-second time period. Find
(a) Pr{Y ≥ 1,250}
(b) Pr{Y ≤ 1.175}
(c) Pr{1,150 ≤ Y ≤ 1,250}
(d) Pr{l,150 ≤ Y ≤ 1,175}