a70
If p,q and r are three consecutive integers, in that order and p>1, is their product divisible by 4?
1. The average of p,q and r is a multiple of 2.
2. \(qr/p\) is an integer
We know that the three integers are consecutive, and that p>1. It's a divisibility problem, so we want to start thinking about what we can deduce regarding divisibility.
When you have three consecutive integers, there are only two possibilities regarding even/odd: the integers either go EVEN-ODD-EVEN, or ODD-EVEN-ODD. Either one of those could be true in this case, given the limited information we have so far.
If the integers go EVEN-ODD-EVEN, then their product will definitely be divisible by 4. After all, p is divisible by 2, and r is divisible by 2, so pr is divisible by 4 (and therefore pqr is divisible by 4.)
If the integers go ODD-EVEN-ODD, their product MIGHT be divisible by 4. If the even integer in the middle is divisible by 4 already, then the product will also be divisible by 4. But if it isn't, the product won't be, either. For instance, 3*4*5 is divisible by 4, but 5*6*7 isn't.
Statement 1 The average of the three numbers is even. Well, they're consecutive, so their average is equal to the middle number, or q. This statement is actually just saying "q is even". If q is even, we know we're looking at the ODD-EVEN-ODD scenario - in which case we don't know whether the product is divisible by 4, as discussed above. Not sufficient.
Statement 2 qr/p is an integer. This is an interesting one. There are other ways to think about it (like case testing), but here's how I approached it.
Since the integers are consecutive, I can write everything in terms of p. The statement really says, (p+1)(p+2)/p is an integer.
Then, I simplified: (p^2 + 3p + 2)/p is an integer.
You can split this up as follows: p^2/p + 3p/p + 2/p is an integer, or in other words, p + 3 + 2/p is an integer.
I already know that p + 3 is an integer, so 2/p also has to be an integer. When is 2 divided by p an integer? Only if p is -2, -1, 1, or 2. But the first three possibilities are off the table, since the question already says that p > 1.
Therefore, this statement really tells us that p = 2. That's sufficient to answer the question.
The answer is B.
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This isn't a 'well-formed' DS question, by the way. In official DS questions, the two statements will never give contradictory information. In this one, statement 1 tells us that p is odd, but statement 2 tells us that p is equal to 2. Since those contradict, you couldn't see a DS question like this one on the test.