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# GMAT: Math 23

120-123, pg. 168. Created by Sal Khan.

## Want to join the conversation?

• Hey guys, For Q123 there might be a simpler way to solve it.

15 people paid 207 including a 15% tax.
So X*1.15 (or 15% of X plus X as 207 is 15% of X plus X) = 207
So X*1.15=207
207/1.15 = 17
207-17=180
\$180 is the total amount pre tax, as 15% of the total X = 17
15 people would pay \$180 total or 180/15 each = 12 • Q.121 I think this problem can be solved by using the combination method as well. 8C2 = 8/2 x 7/1 = 28

(1 vote) • q:121 combinatorics (8*7)/(2*1) • how is the formulas mixed? • For question 123, I completely understand everything that you did, but I am curious why you cannot just multiply \$207 by 85%, since it is the reciprocal of the 15% gratuity. The answer I get from doing it this way is \$11.73, which is wrong-but hoping that you can still explain it to me so that it sticks in my mind for the exam! Thanks! :) 