if a person gets 12 dollars every year and a other person gets 21 dollars the first person is 10 and the second is 8 after those years how many yeaars will it take to get the same amount of money?
+1107 http://www.geteasysolution.com/least-common-miltiple-lcm-of-12-and-21
This is where I got it from, I am only a 7th grader who doesn't pay attention in class... 
Your question is faulty! They will never have the same amount of money as long as they are both alive!. If the one who gets $21 a year dies and the other continues to get his $12 every year, then there a possibility that he will reach the same amount. But, it also depends on: when does he die?
If he dies 4 years from now, he will have accumulated: 4 x $21 =$84, and the other will have the same amount of money 3 years after the death, or 7 years from now: 7 x $12= $84.
