Official Solution: Ann and Bob each randomly select an integer from the integers \(x\) to \(y\), inclusive. What is the probability that the integer Ann selects is greater than the one Bob selects? (1) \(y - x = 9\)
This implies they are choosing a number from a set of 10 integers, for example, from 1 to 10, inclusive.
Then:
• Total outcomes = 10 * 10 = 100
• Equal cases (both choose the same number) = 10
• Remaining cases = 90
• Out of those 90, half will have Ann’s number < Bob’s, and half will have Ann’s number > Bob’s.
• So, required probability = 45/100 = 9/20
As you can see, the only thing we needed to know is the sample size. Sufficient.
(2) \(y = -20\)
This is clearly insufficient. We have no idea how many integers they’re choosing from.
Answer: A