Monday, September 3, 2012

Answer It

Here is another post that made its way around the internet. I found it on facebook. It is a great warmup for the 7th grade math student reviewing Order of Operations (often known as PEMDAS - a.k.a. "Please Excuse My Dear Aunt Sally", standing for: Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction).

Many adults missed this question and 'verified' the incorrect answers on their computers and calculators (simple, or older, calculators are not programmed to manage the mathematical Order of Operations). An interesting experiment is to type this mathematical sentence on a simple calculator and also type it into a scientific calculator. You will get two different answers. (It is important to type the whole sentence and then hit the equal button, otherwise hitting enter or equal acts like inserting parentheses into the sentence and this will change your answer).

There was a lot of debate about 'clarifying' the mathematical sentence by using parentheses. I shuddered to read statements like, "It depends upon how you 'interpret' the mathematical sentence." One of the great aspects of mathematics is that there are agreed upon rules that disallow the need to 'interpret'. Interestingly, and a testament to how different brains work, many people remembered the expression, "Please excuse my dear aunt Sally", but couldn't apply PEMDAS correctly and got the answer wrong.

Spoiler alert!!! The answer is 7.

Many people got 1, and some people got 5 for an answer.

Explanation:
Multiplication and Division are on the same 'level' of the operations 'ladder'. PEMDAS should actually look like
P
E
MD
AS
Multiplication and Division are done by whichever occurs first in the mathematical sentence, and the same applies for Addition and Subtraction. Either way, Multiplication and Division need to occur before Addition and Subtraction.

Therefore, our problem is reduced to 6 - 0 + 1 = 7.


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