Does the integer k have a factor p such that 1 ? (k > 4! 13! + 2 leq k...
GMAT Data Sufficiency : (DS) Questions
Does the integer \(\mathrm{k}\) have a factor \(\mathrm{p}\) such that \(1 < \mathrm{p} < \mathrm{k}\)?
- \(\mathrm{k} > 4!\)
- \(13! + 2 \leq \mathrm{k} \leq 13! + 13\)
Understanding the Question
We need to determine whether integer k has a factor p such that \(1 < \mathrm{p} < \mathrm{k}\).
In simpler terms: Is k a composite number?
- If k is composite → It has factors other than 1 and itself → Answer is YES
- If k is prime or k = 1 → No such factors exist → Answer is NO
For this yes/no question, we need definitive information about whether k is composite.
Analyzing Statement 1
Statement 1: \(\mathrm{k} > 4! = 24\)
This means \(\mathrm{k} \geq 25\). Let's test whether all numbers ≥ 25 are composite:
- If \(\mathrm{k} = 25 = 5^2\), then 5 is a factor where \(1 < 5 < 25\) → Answer is YES
- If \(\mathrm{k} = 29\) (prime), then no factor exists where \(1 < \mathrm{p} < 29\) → Answer is NO
Since we can get both YES and NO answers, Statement 1 is NOT sufficient.
This eliminates choices A and D.
Analyzing Statement 2
Starting fresh—we must forget Statement 1 completely.
Statement 2: \(13! + 2 \leq \mathrm{k} \leq 13! + 13\)
This gives us a very specific range. Any k in this range can be written as \(\mathrm{k} = 13! + \mathrm{a}\), where \(2 \leq \mathrm{a} \leq 13\).
Key Insight: What factors does 13! have?
- \(13! = 1 \times 2 \times 3 \times 4 \times \ldots \times 13\)
- Therefore, 13! is divisible by every integer from 2 to 13
This creates a powerful pattern:
- When \(\mathrm{k} = 13! + 2\), since 13! is divisible by 2, we have \(\mathrm{k} \equiv 2 \pmod{2}\), so 2 divides k
- When \(\mathrm{k} = 13! + 3\), since 13! is divisible by 3, we have \(\mathrm{k} \equiv 3 \pmod{3}\), so 3 divides k
- When \(\mathrm{k} = 13! + 4\), since 13! is divisible by 4, we have \(\mathrm{k} \equiv 4 \pmod{4}\), so 4 divides k
- This pattern continues for every value in our range
Since \(13! = 6,227,020,800\) (huge!) and \(\mathrm{a} \leq 13\), we definitely have \(1 < \mathrm{a} < \mathrm{k}\).
Therefore, every integer in this range is composite.
The answer is definitively YES. Statement 2 is sufficient.
[STOP - Sufficient!]
The Answer: B
Statement 1 alone: Not sufficient (both composite and prime numbers exist above 24)
Statement 2 alone: Sufficient (all numbers in the range are composite)
Answer: B - Statement 2 alone is sufficient, but Statement 1 alone is not sufficient.