Science Popularization Masterpieces of China: Helping You Learn Mathematics

Author: Zhang Jingzhong
Publisher:
Publish Date: 2002-01-01
Features: The commutative law in arithmetic is just as useful in daily life. However, you can't misuse it either. The story of the monkey eating chestnuts is, of course, made up and not a factual account. But the zookeeper who feeds the animals knows; when feeding pigs, start with roughage and then add concentrated feed to make them eat better, sleep better, and grow faster. The commutative law doesn't apply here. There are also some things where the order is fundamentally unchangeable. Putting on socks first and then shoes is correct. But what if you put on shoes first and then socks? It would look ridiculous. Unscrew the pen cap, fill it with ink, and then write—this is correct. The reverse is impossible.