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GMATPrep Test 1 Many questions....

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GMATPrep Test 1 Many questions....

by fuji727 » Fri Dec 18, 2015 8:37 am
Hi everyone!

I'm hoping that someone can help me out with these questions and what the thinking process should be to solve problems such as these. The GMAT Prep unfortuantely doesn't give explanations and I can't seem to understand/figure them out! Thank you so much!!


1. If the sum of three different numbers is 54, what is the largest number?
(1) The largest number is twice the smallest number
(2) The sum of the two smaller numbers is 30

2. What is the remainder when the positive integer n is divided by 6?
(1) n is a multiple of 5
(2) n is a mulitple of 12

3. If p is a positive integer, what is the value of p?
(1) p/4 is a prime number
(2) p is divisble by three

**For this question isn't it A, because p has to be 2?
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by [email protected] » Fri Dec 18, 2015 10:40 am
Hi fuji727,

It's best to post one question per thread. In that way, the conversation can stay focused on that one prompt (and you can avoid a mash-up of several conversations at once).

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by Max@Math Revolution » Mon Dec 21, 2015 9:16 pm
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.


1. If the sum of three different numbers is 54, what is the largest number?
(1) The largest number is twice the smallest number
(2) The sum of the two smaller numbers is 30

-> When you modify the original condition and the question, based on a<b<c, you only need to know a+b from a+b+c=54, c=54-(a+b). Since 2) a+b=30, c=54-30=24, which is unique and sufficient. Therefore the answer is B.

2. What is the remainder when the positive integer n is divided by 6?
(1) n is a multiple of 5
(2) n is a mulitple of 12

-> In the original condition, there is 1 variable(n), which should match with the number of equations. So you need 1 more equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer. 1) n=5, r=5/ n=30, r=0, which is not unique and therefore not sufficient.
In 2), n=12,24,36..... and all r=0 is unique and sufficient. Therefore the answer is B.

3. If p is a positive integer, what is the value of p?
(1) p/4 is a prime number
(2) p is divisble by three

In the original condition, there is 1 variable(n), which should match with the number of equations. So you need 1 more equation. For 1) 1 equation, for 2) 1 equation, which is likely to make D the answer. For 1), p=8, 12 is not unique and not sufficient. For 2), p=3, 12 is not unique and not sufficient. In 1) & 2), only p=12 is possible, which is unique and sufficient. Therefore the answer is B.
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