If S is a set of 3r distinct positive integers and the range of S is 15 – r, how many possible values of r are there?The minimum possible value of the range is 0. So, 15 - r ≥ 0. Thus, r ≤ 15.
Also, as r increases, the range decreases.
Meanwhile, since the number of integers in the set is 3r, as r increases, the number of integers in the set increases.
So, as the range decreases, the number of integers in the set increases. We see that this dynamic limits the possible number of integers in the set to a relatively small value. So, using that information along with the answer choices, we can tell that we can quickly answer this question by just testing values.
r = 0Range = 15 - 0 = 15
Number of Integers in the Set = 3 × 0 = 0
Impossible (because a set of zero distinct integers cannot have a range of 15)
r = 1Range = 15 - 1 = 14
Number of Integers in the Set = 3 × 1 = 3
Possible
r = 2Range = 15 - 2 = 13
Number of Integers in the Set = 3 × 2 = 6
Possible
r = 3Range = 15 - 3 = 12
Number of Integers in the Set = 3 × 3 = 9
Possible
r = 4Range = 15 - 4 = 11
Number of Integers in the Set = 3 × 4 = 12
Possible (because the first and last of 12 consecutive integers can be 11 apart)
We can see that since, if we go higher, 3r will be much greater than 15 - r, we can stop at r = 4.
So, there are four possible values of r: 1, 2, 3, and 4.
A. 1
B. 2
C. 3
D. 4
E. 5Correct answer:
D