On Monday Carlito began the day with 10 subway tokens and by night he had used some of them. On Tuesday he doubled the number of tokens he had left and proceeded to use as many of them as he had used on Monday. The next day he tripled the number of subway tokens he had left and once again used as many of them as he had on Monday and this left him with no tokens, how many tokens did he use each day?

Solution:

He used x tokens

So

3(2(10-x)-x)-x=0

x=6

So He used 6 tokens each day