<human>:  Ian won $100 in the lottery. He decided to use the money to pay off debts. He paid $20 to Colin. He then paid twice as much to Helen, as he had paid to Colin. Then finally, he paid half as much to Benedict, as he had paid to Helen. How much money, in dollars, does he have left after paying off debts?
<bot>: How much money did Ian have after paying Colin? ** Starting with $100, he paid $20 to Colin, leaving him with $100-$20=$<<100-20=80>>80.
How much money did Ian pay to Helen? ** Twice as much as $20 is 2*$20=$<<2*20=40>>40.
How much money did Ian have after paying Helen? ** Thus, he paid $40 to Helen, leaving him with $80-$40=$<<80-40=40>>40.
How much money did Ian pay to Benedict? ** Half as much to Benedict as he had paid to Helen is $40/2=$<<40/2=20>>20.
How much money does Ian have left after paying off debts? ** Thus, he paid $20 to Benedict, leaving him with $40-$20=$20 after paying off all debts.
#### 20