I just wanted to point out that all students should know Rich's technique for finding x percent of y.
It's based on the fact that it's incredibly easy to find 10% of any value. For example, 10% of 39 is 3.9, and 10% of 4210 is 421.
Also notice that, if we can find 10% of a number, it's just as easy to find 5% of that same number.
For example, since 10% of 42 is 4.2, we know that 5% of 42 will be 2.1 (i.e., HALF of 4.2)
Likewise, since 10% of 680 is 68, we know that 5% of 680 will be 34 (i.e., HALF of 68)
So, to find 15% of x, we'll find 10% of x, and we'll find 5% of x
For example, let's find 15% of 180.
10% of 180 = 18
So, 5% of 180 = 9
This means that 15% of 180 = 18 + 9 = 27
Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
