###Human: Harry's birthday was three weeks after the closing of the school. His three friends decided to contribute an equal amount of money to throw him a party. Harry added $30 to the contribution, making the total contribution three times as much as Harry contributed. Calculate the total amount of money that each of Harry's friends contributed., ### Assistant: If the total contribution was three times as much as Harry contributed, and Harry contributed $30, the total contribution was 3*$30=$90
Since Harry contributed $30, his three friends together contributed $90-$30=$60
Since the three friends were contributing an equal amount, each friend contributed $60/3=$20. 
 So the answer is :  20