Mrs. Young buys a 300 piece puzzle set for her three sons.  She divides the pieces evenly to the three boys.  Reyn can place 25 pieces into the puzzle picture.  Rhys places twice as much as Reyn.  Rory places three times as much as Reyn. Altogether, how many puzzle pieces are still left to be placed?
How many pieces does each son receive? ** Each son receives 300 / 3 = <<300/3=100>>100 pieces.
How many pieces does Rhys place? ** Rhys places 25 x 2 = <<25*2=50>>50 pieces.
How many pieces does Rory place? ** Rory places 25 x 3 = <<25*3=75>>75 pieces.
How many pieces do all three boys place? ** All three boys place 25 + 50 + 75 = <<25+50+75=150>>150 pieces.
How many pieces are still left to be placed? ** The boys have not placed 300 - 150 = <<300-150=150>>150 pieces.
#### 150