GRE Math Tricks: Converting fractions to percents without long division

Here we'll examine a technique for converting fractions to percents without resorting to
long division.
So let's say that in the course of solving some problem, we come to this fraction, and
we now want to convert this to a percent.
Our technique will be to rewrite this fraction as a new fraction with denominator 100.
To perform this conversion, we must multiply 32 by approximately 3. Now unfortunately,
32 times 3 does not equal 100. 32 times 3 equals 96.
So really, we must multiply 32 by a number slightly larger than 3.
Now if we multiply our denominator by a number slightly larger than 3, we must also multiply
our numerator by a number slightly larger than 3.
When we do this, we get a number slightly larger than 21.
And this is equal to a number slightly larger than 21%.
Now when we look at our answer choices, we see our answer must be D, since it is slightly
larger than 21%.
Let's try another example.
Let's convert this fraction to a percent.
Well, we want to rewrite this fraction as a new fraction with denominator 100.
To do this, we must multiply 51 by approximately 2. Now 51 times 2 is greater than 100--51
times 2 is 102. So we want to multiply 51 by a number slightly less than 2.
This means we must multiply 22 by a number slightly less than 2 as well.
And when we do this, we get a number slightly less than 44.
And this equals a number less than 44%.
So looking at our answer choices, we see that our answer must be A.