Math Help Forum - View Single Post - Simple PEMDAS ?

masters · #2 April 25th, 2009, 05:51 PM

Quote:

Originally Posted by garms

Hi all,

Been a while since I went through my Order of Operations and I have a problem that I know the answer to but I need someone to help me see why the answer is correct... if that makes sense.

Problem is 3-4[-10-4(-5)]
Correct Answer is supposed to be: -37

1) I know to work inside parens first...
2) Since there is no real work inside the Parenthesis... this is where I mess up I think... I would do Multiplication next... so I would take the -4 * -5 and get +20... correct?
3) Next I would then take the -10 * +20... I know this can't be right.. so I try again... using only the +4 * (-5) and that gets me closer but doesn't really make sense to me because the -10 - 4 is actually a negative four right? Arrggh!
4) So then -10 * -20 doesn't work either... please help!

Step by step is ok... but really need the Why. Thanks in advance for your assistance and advice.

Hi garms,

Let's take this step by step:

$3-4[-10{\color{red}-4(-5)}]$

Do the operation in red first:

$3-4[-10{\color{red}+20}]$

Next, simplify what's within the brackets:

$3-4[+10]$

Next, multiply by -4:

$3-40$

And you get your desired result.