Science Popularization Masterpieces from China: Helping You Learn Mathematics

Author: Zhang Jingzhong
Publisher:
Publish Date: 2002-10-01
Features: The commutative law in arithmetic is equally 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, first give them roughage, then add concentrated feed, so they eat better and become fatter, sleep well, and grow faster. The commutative law doesn't hold here. There are also some things where the order cannot be exchanged at all. Putting on socks before shoes is correct. Reversing it—putting on shoes before socks—makes no sense. Unscrewing a pen cap, filling it with ink, and then writing is correct. Reversing it is impossible.