$$50$$ children want to purchase the special football club shirt of their school. The shirt costs £$$10$$, or £$$15$$ if you wish to have your name put onto the back. Together the children pay £$$555$$. How many of the children paid to have their name put onto the shirts? 
Overseas Competition->Knowledge Point->Word Problem Modules->Chicken-Rabbit Problems->Solving Chicken-Rabbit Problems by Using Hypothesis->Basic Type->Non-typical Types