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How are you supposed to actually learn how to solve these questions? I could spend an hour trying to solve some of the questions and even that I will probably still be stumped....is there a good way to learn the tricks to solve these toughies?
These questions are for practice. You don't have to 'learn' the method for each one. First figure out if you are ready for them i.e. can you solve the easier questions comfortably? Are your basics in place? Let's say, can you solve most OG12 questions in less than a minute? Once you know that you have tamed the easy ones, then go for the difficult ones. You just have to try and solve them and if you are unable to, then check out the explanations. If you have doubts in a question, post it and people will give their take on it. With every new question, you will learn something new. You will get different ways of figuring out the answer since most people have their favored mechanisms. Finally most questions in GMAT are based on a handful of basics. Once you have seen 20 different applications of the same concept, it doesn't matter how the concept is presented to you. You will know how to deal with it.
to those people who have seen/worked on these questions..can you please share the source of these questions?are they GMATlike? are they worth the time spent in solving these problems?
It depends on 2 factors: 1. your interest in solving 2. time left for actual GMAT exam: you have ample time, u can go ahead and solve these, else just concentrate on individual questions being posted in the forum.
AB + CD = AAA, where AB and CD are two-digit numbers and AAA is a three digit number; A, B, C, and D are distinct positive integers. In the addition problem above, what is the value of C?
In this - how can u say that AAA should be 111 - i dint get it.
A B +C D ______ A A A
Notice here that B+D ends with A (there could be a carry over so I cannot say that B+D = A) Also, A + C ends with A. When can this happen? e.g. Think 2 + x = .....2 What can you say about x? We can say that it must end with 0. Only then will you have 2 at the end.
Since all letters represent positive integers, C cannot be 0. Then it must be 9 and there must have been a carry over from previous addition to make 10. Then A + 10 will end with A and there will be a carry over of 1 which will appear as the hundred's digit. Since the hundred's digit is A, it must be equal to 1.