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SASMO 2016 P2 Q6  Uncle John has a farm. His wife and his two sons are staying with him in the farm. They raise 10 cows and 20 chickens. How many total legs are there in the farm? 
Overseas Competition->Knowledge Point->Counting Modules->Law of Addition and Multiplication
10 x 4 + 20 x 2 + 2 + 2 + 4 = 88. 