1

## Please Excuse My Dear Aunt Sally

Published on Thursday, May 23, 2013 in , , , ,

The order of operations is one of those things in elementary school math that probably caused you great frustration.

The order of operations, as taught in the US, is: Parentheses, Exponents, Multiplication, Division, Addition, Subtraction. This is usually taught with a mnemonic, such as PEMDAS (the first letters), or “Please Excuse My Dear Aunt Sally” (the first letters with an easily remembered phrase). Elsewhere, you may have learned BEDMAS (B is for Brackets, same as parentheses), BODMAS (O is for Orders, same as exponents), or BIDMAS (I is for Indices, same as exponents).

Having dealt with them before, you may be glad that you finally mastered the order of operations. However, they do still hold quite a few surprises.

The first surprise is that, as explained in the minutephysics video below, the order of operations is wrong. More accurately, it's not so much wrong as it is a weak attempt to mechanize the logic of how to handle mathematical equations.

Once you think you've got a handle on the ideas behind the order of operations, it's time to put your understanding to the test.

In what they deem to be their hardest puzzle ever, Scam School challenges you in just this way. Below is a number puzzle in which all the numbers are provided for you. The challenge is to add in the right operations so that each set of numbers total 6. Watch the instructions up to about the 3:30 mark, and try and solve it without any of the hints given later.

I'm proud to say that I managed to get all 10 answers working on my own without hints. I did, however, come up with a different approach for the 8s. As long as you've already tried and either succeeded or given up, you can see my answer guilt-free.

As Diamond Jim Tyler and Brian Brushwood mention, this puzzle doesn't seem to have hit the states until now. It is a good one to have in your arsenal, especially once this episode is several months old. I can't be sure, of course, but I'd like to think Martin Gardner would've appreciated this puzzle.

### 1 Response to Please Excuse My Dear Aunt Sally

Anonymous
9:40 PM

8-sqrt(sqrt(8+8))