There have been many metric systems, or systems of measurement. On 7 April 1795 the National Convention of France decreed new "Republican Measures" to be legal measures in France. The units of measurement included the meter, liter, and gram; the prefixes centi, deci, deca, hecto, and kilo were also sanctioned. This was the decimal system of measurement or the decimal metric system. It has survived practically unchanged and now is known simply as the metric system. The latest version of the system is the International System of Units or SI for short.

Many people think of algebra as dealing with solving equations that have letters and numbers, and that it is completely unrelated to anything outside the math classroom. Also, teachers have a difficult time motivating students to learn algebra. I have found that not only are number/magic puzzles quite common outside the classroom, but also that they motivate students, and that teachers can successfully use such number puzzles as an interesting lead-in to algebra. Here I discuss two number/magic puzzles that can be demystified and explained by using algebra.