## Tuesday, March 19, 2013

### Weird Word of the Week: Obelus

The obelus is the mathematical symbol for the division operation, the ÷ symbol.

Madame L came upon this word in an article about a math problem which looks easy but which has different potential answers depending on how you interpret those good old math rule you learned in school, you know, the PEMDAS rule:

Parenthesis first, Exponents, Multiplication and Division (left to right), and Addition and Subtraction (left to right).

Using this method to solve the problem 6 ÷ 2(1+2), Madame L gets the answer 9.  Here's what the calculation looks like: 6 ÷ 2(1+2) = 6 ÷ 2 × (1+2) = 6 ÷ 2 × 3 = 3 × 3 = 9

Another method is to divide everything to the left of the ÷ symbol by everything to the right of it.  Using this method to solve the problem 6 ÷ 2(1+2), solving the 2(1+2) part of the equation first, Madame L gets the answer 1.

Madame L, always an iconoclast, is pleased to find an example of the "pure logic" of math giving different answers to the same question.