If P is the sum of all the positive odd integers less than 50 and Q is the sum of all positive even integers less than 50, then P - Q =
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lol this one looked scary but then I just paired them up... like 1 and 2, 3 and 4... each pair gives -1, and there are 24 such pairs? wait, but 49 is left over. so -24 + 49? that's 25. took me a sec to see the pairing trick.
yesss the leftover odd number is the key, I kept forgetting about it and kept getting -24. classic trap answer right there.
same! I almost picked -24 too. sneaky answer choices lol
What it tests
Your command of divisibility, primes, factors, parity, and how the GMAT tests properties of integers.
Common trap
Forgetting that 1 is not prime, that 0 is divisible by every integer, or that negative numbers flip your assumptions.