其它
When Coco the Caterpillar is not sleeping, he eats $$5$$ grams of leaves per hour. Yesterday he slept $$20$$ hours. How many grams of leaves did he eat yesterday? 
Overseas Competition->Knowledge Point->Counting Modules->Law of Addition and Multiplication
Yesterday he did not sleep for $$24 - 20 = 4$$ hours, so he ate $$4 \times 5 = 20$$ grams of leaves. 