Form the prompt, I know that two people are picking an integer from a set of consecutive integers ("from x to y"), inclusive, and they can pick the same integer.
Using statement (1):
We are given the range of the set of integers & can find the number of possible integers they can pick from. Consider how:
the number of integers in a set of consecutive integers = Max - Min + 1
= y - x + 1
= 10
Thus, the there are 10 integers to pick from, and we can find the probability of Ann picking a larger integer than Bon by applying the probability formula where:
P(Ann > Bob) = Number of outcomes where Ann's number is bigger than Bob's / the number of total possible outcomes
At this point, I would quickly consider whether I need anymore info to be able to calculate this and once I realise that I don't, I can move on to statement (2) and conclude that
statement (1) alone is sufficient.
Using statement (2):
I know the y value but I can't calculate any probabilities without knowing the x value or the range between the two values. Thus,
statement (2) alone is NOT sufficient.
Answer: A) Statement one alone is sufficientTo elaborate on statement (1)'s sufficiency:
If Bob picks x (the smallest number), there are 9 ways in which Ann can pick a larger number
If Bob picks x+1 (the 2nd smallest number), there are 8 ways in which Ann can pick a larger number
etc.....
If Bob picks x + 8 (the 2nd largest number, or y-1), there is 1 way in which Ann can pick a larger number.
Because Bob can pick x OR he can pick x+1 etc. we will add all the outcomes (9+8+7+...+1) to get 45 favourable outcomes
Given Bob and Ann can pick the same number, the total number of possible outcomes is 10C1 x 10C1 = 100
Thus,
the probability of Ann picking a larger number than Bob is 45/100 = 0.45The reason we don't need anymore info is that even if y is negative and therefore x is actually the smaller number, the probability is still the same.
Say for example that y = -20 and thus x = -29;
if Bob picks -21 there is 1 way in which Ann can pick a larger number
If Bob picks -22 there are 2 ways in which Ann can pick a larger number
etc.
We are still left with 45 favourable outcomes out of 100 total possible outcomes.