其它
THere are 3 families in my neighbourhood with three children each; two of the families have twins. All twins are boys. At most how many girls are in these families? 
Overseas Competition->Knowledge Point->Word Problem Modules->Applying Addition and Subtraction->Simple Addition and Subtraction
There are 3 families with 3 children = 3 x 3=9.  If there are 2 twin boys, 2 x 2 = 4, 0-4=5. 