負數總比沒有好：乘法

It was not too long ago--relatively speaking--that the concept of zero was very controversial. Part of the reason our word for zero comes from Arabic is because the Islamic mathematicians used it for Algebra, another Arabic-origin word. Well out of this single number for nothing was born an entire set of numbers, all of them less than nothing! This is the first set of truly abstract concepts in mathematics introduced to children. It took math and engineering experts thousands of years to wrap their heads around them, so it's okay to find them difficult too.

In this follow-up 2-hour class we'll now multiply negative numbers (division is almost identical). While adding and subtracting negative numbers has a certain physical manifestation that makes sense, multiplying something that doesn't exist is indeed weird. All multiplication is just a shorthand for repeated addition, so a large part of this class will be learning how to rethink of a multiplication problem as an addition or subtraction problem. Adding in negative variables is a natural thing to add at this time.

Knowledge of adding and subtraction negative numbers is a prerequisite. If your learner takes the companion course covering this topic, I suggest waiting about a month to take this course. Otherwise, it's easy to mix up the two topics. 

We'll also do some more binary logic puzzles, learn a new card game, and talk about how computers use negative numbers.