In addition to the blood types A, B, AB , and O, a person’s blood may be classified as Rh positive or Rh negative. In the United States, about 15% of the white population is Rh negative, while the percent is much lower in other racial groups. The director of a blood bank wants to estimate the probability that in a random group of 50 unrelated white donors, at least 8 will have Rh negative blood. If she generates random numbers to simulate this problem, how could she assign the numbers to the two blood types? A. Assign the numbers 0 through 8.5 to people with Rh positive blood and the numbers 8.6 through 9.9 to people with Rh negative blood. B. Assign the integers 00 through 84 to people with Rh negative blood and the integers 85 through 99 to people with Rh positive blood. C. Assign the integers 00 through 85 to people with Rh positive blood and integers 86 through 99 to people with Rh negative blood. D. Assign the integers 00 through 84 to people with Rh positive blood and the integers 85 through 99 to people with Rh negative blood.

If you want to simulate a percentage, you need to have 100 possible events. If you use 1-100, the range will be 1-85 for positive and 86-100 for negative. Looking at the option its all using 99 as the ceiling, so we use 0-99. Since we use 0, then you have to subtract 1 on the number range. There are 85% chance of Rh-positive, so the assigned number will be

1 through 85

(1-1) through (85-1)

0 through 84

The range for Rh-negative will be:

86 through 100

86-1 through 100-1

85 through 99

Option B is wrong because it assigns 00 through 84 to people with Rh negative blood, not Rh-positive. The right answer will be option D.