其它
SASMO 2014 P2 Q6  A shop sells sweets where every 3 sweet wrappers can be excanged for one more sweet. Ali has enough money to buy only 7 sweets. What is the biggest number of sweets that he can get from the shop? 
Overseas Competition->Knowledge Point->Counting Modules->Law of Addition and Multiplication
7 = 3 + 3 + 1 + (1) + (1) + (1) = 10 