i know the same question with 75, i guess it works for 30 as well, but the question is: 3 men go to a restaurant and the total bill is $75. All three decide to pitch in 25 each to pay the bill. As there is a special that day, the manager gives them a $5 discount, thus $5 is returned to them from the 75. The three men decide to put 2 of the 5 dollars that was returned, as a tip and they split the remaining $3 among themselves, so that each got $1 back. As the men had paid $25 earlier, and now got a dollar back, they effectively paid $24. But, then, 24x3=72, plus the $2 tip = $74. But they had paid $75 earlier, where did the $1 go ? cheers, nepalikochoro