Starting with $100, he paid $20 to Colin, leaving him with $100-$20=$<<100-20=80>>80.
Twice as much as $20 is 2*$20=$<<2*20=40>>40.
Thus, he paid $40 to Helen, leaving him with $80-$40=$<<80-40=40>>40.
Half as much to Benedict as he had paid to Helen is $40/2=$<<40/2=20>>20.
Thus, he paid $20 to Benedict, leaving him with $40-$20=$20 after paying off all debts.
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