其它
SASMO 2014 P2 Q9  Two $1 coins and ten 50c coins are randomly distributed among 4 children such that each child receives the same number of coins. What is the difference between the biggest amount and the smallest amount a child can receive? 
Overseas Competition->Knowledge Point->Counting Modules->Law of Addition and Multiplication
There are a total of 2+10 = 12 coins. so each child receives 12/4 = 3 coins.  Largest possible is $1 + $1 +50c= $2.50.  smallest possible is 50c + 50c + 50c= $1.50  $2.50 - $1.50 = $1 