question: In a set of magicians cards, there are 15 red cards, and 60% more green cards. Yellow cards are as many, as the sum of red and green cards. How many cards of all mentioned colors are there?
answer: There are 60/100 * 15 = <<60/100*15=9>>9 more green cards than red cards.
  Which means there are 15 + 9 = <<15+9=24>>24 green cards.
  Yellow cards make up to 15 + 24 = <<15+24=39>>39 cards.
  So in total, there are 39 + 39 = <<39+39=78>>78 cards of different colors.
  #### 78