Math problem, cake 3 yuan. How much is it to buy seven cakes?
3 times 7 equals 2 1 yuan, which is different if it is for promotion. Generally, it is 2 1 yuan, and this oxygen can also be counted as a ***7. A 3 yuan is the sum of 7 3+3+3+3+3+3+3 = 3× 7 = 2 1. I hope to adopt O(∩_∩)