GMAT Quant Tip- keep things in primes

One way to ensure that you are working your way through problems as quickly as you can is to keep numbers in their simplest form (ie primes). This way,  you know when you can quickly eliminate common factors to figure out the answer.  When you see a problem like this:

91x= 143*70

you might be tempted to multiply out 143*70 and then divide by 91.  However, this isn’t the fastest way to do that.  If we reduce it to primes, we will see that the problem is actually

13*7x=11*13*7*10

We can then eliminate the 13 and the 7 from both sides and we know immediately that x is 110.  When you are working through complicated problems that involve a lot of multiplication, don’t immediately try to multiply those numbers out.  Keep them in their most basic forms while working through the problem. 

This is especially important when you have problems with large fractions.  You can very easily simplify the fraction by dividing out common primes.

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