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?
Each son receives 300 / 3 = <<300/3=100>>100 pieces.
Rhys places 25 x 2 = <<25*2=50>>50 pieces.
Rory places 25 x 3 = <<25*3=75>>75 pieces.
All three boys place 25 + 50 + 75 = <<25+50+75=150>>150 pieces.
The boys have not placed 300 - 150 = <<300-150=150>>150 pieces.
#### 150