The key concept being tested here is range with a variable element — specifically, what happens to the range of a set when one value is unknown and can shift the maximum or minimum.
The big trap most people fall into: they assume x is just "some middle value" and the range stays fixed at 11. The whole question hinges on recognizing that x can be the new maximum, the new minimum, or somewhere in the middle — and each case gives a different range formula.
Step 1 — Identify the range for each case of x.
The known values are 7, –4, 2, 3. Without x:
- Current max = 7, current min = –4, so the "interior" range = 11.
Three cases based on where x falls:
- Case A (x ≥ 7): x is the new max → Range = x – (–4) = x + 4
- Case B (x ≤ –4): x is the new min → Range = 7 – x
- Case C (–4 < x < 7): range stays = 11
Step 2 — Test Statement I: 3x – 12
Try Case A (x ≥ 7): Set 3x – 12 = x + 4 → 2x = 16 → x = 8. Since 8 ≥ 7 and is an integer, ✓ this works.
Statement I is possible.
Step 3 — Test Statement II: 10
- Case A: x + 4 = 10 → x = 6. But 6 < 7, contradiction.
- Case B: 7 – x = 10 → x = –3. But –3 > –4, contradiction.
- Case C: Range = 11 ≠ 10.
Statement II is never possible.
Step 4 — Test Statement III: 2x + 25
Try Case B (x ≤ –4): Set 2x + 25 = 7 – x → 3x = –18 → x = –6. Since –6 ≤ –4 and is an integer, check: range = 7 – (–6) = 13, and 2(–6) + 25 = 13. ✓
Statement III is possible.
Answer: C (I and III only)
Takeaway: Whenever a set contains an unknown x, always split into three cases — x is the new max, x is the new min, or x is interior — and test each expression against each case. Skipping even one case is how you miss an answer.