to my knowledge there are 3 different sources for OG 12 companion.
1. GmatFix.com
2. Gmathacks.com
3. Manhattan Gmat Companion (
https://www.manhattangmat.com/storeitems ... 7&catid=10)
I purchased the Manhattan GMAT companion book and I must say I have found it pretty helpful on some of the answers. what I also like about it is that it categorizes the questions based on how hard it is ( ex: 500-600 / 600-700 )
Let me give you an example for you to get a sense of a difference.
Try the question 106 on page 167 of OG 12
now look at the explanation for it on the back of OG.
After you have reviewed the explanation, read the below which is the explanation from the Manhattan Companion guide.
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Difficulty: 600-700
In this Divisibility problem, we need to recognize that, in an expresion such as x/y=96.12, the remainder is equal to 0.12y. In other words, the remainder must be equal to the decimal part of the quotient times the divisor, which in this case is y.
For example, 32/5=6.4 as a Decimal. In remainder notation, 32/5 = 6, with remainder 2. Notice that the remainder (2) must be equal to the decimal portion (0.4) times the divisor (5). In other words, 2=0.4*5
Since our remainder must be equal to 0.12y and we are also told that the remainder is 9, set 0.12y equal to 9 and solve for y. To reduce the fraction quickly, move decimal points.
0.12y = 9
y = 9/0.12 = 900/12 = 75
Correct Answer : B
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Hope this helps
