mikemcgarry wrote:
closed271 wrote:
Is there any reason why you start with C while using POE? What if the numbers are not given in a particular order (ascending here)? Do you use the same strategy in other question types?
On official GMAT problems, if the answer choices are all single numbers, those numbers will be in numerical order. This is true on all official material and all high quality material, and therefore it's an excellent test of how authentic a given prep source is --- if you see a number of questions with the answers out of order, that's a red flag --- you should question whether that source is trustworthy. Some GMAT prep sources are excellent, and some are not worth the paper on which they are printed.
The reason we start with the middle answer (i.e. (C) on official material) is so that we know
which way to go if our first choice is not right. Consider this hypothetical question:
Frank started with X money. He bought blah blah, blah blah, blah % of blah, etc etc and was left with $41.50 in cash after those purchases. What was Frank's original starting amount?
(A) $100
(B) $120
(C) $150
(D) $180
(E) $200I will start with (C) 150 ----- if by chance I'm right, that's great. If I wind up with
more leftover cash than $41.50, I know I started with too much --- I can eliminate (C) & (D) & (E). If I wind up with
less leftover cash than $41.50, I know I started with too little --- I can eliminate (A) & (B) & (C). Does that make sense?
Mike
I agree with Mike that Plugging In The Answers is a great way to go on this question and others for which the instinct is to start setting up complex algebraic equations. One tweak (an important one, I think): rather than starting with C, I suggest starting with B or D. Here's why.
If A is correct: The C-first approach requires you to test two answer choices, C and then either A or B. The B-first approach only requires you to test one answer choice, B and then there is only left that is smaller.
B-first approach wins.If B is correct: The C-first approach requires you to test two answer choices, C and then either A or B. The B-first approach only requires you to test one answer choice.
B-first approach wins.If C is correct: The C-first approach requires you to test one answer choice. The B-first approach requires you to test two answer choices. You do B first and find that you need something larger. You're down to C, D, and E. If you try D and need something smaller, C is the only option available.
C-first approach wins.If D is correct: Both approaches require you to test two answer choices. No winner.
If E is correct: Both approaches require you to test two answer choices. No winner.
And an additional benefit of B-and-D is that sometimes you'll test an answer choice, it won't be right, and you won't be positive whether you need something smaller or larger. In that case, the C-first approach could mean having to test ass many as three answer choices (if you go the wrong direction in choosing which to try second and are therefore still left with two). B-first still only requires a maximum of two. If you need something between B and D, it's C. If you went the wrong direction in trying D after B, it's A. If you got closer, but not all the way there, it's E.