1-3x4+7=?

1-3x4+7=?
Discuss.

reply to post by grey580


the answer is -4, whats the point of this? lol

reply to post by grey580


or
-18
...
did I forget how to do basic math???

reply to post by GypsK


PEMDAS rule
Parentheses / Exponents / Multiplication & Division / Addition & Subtraction

1-(3x4)+7 = 1-12+7 = -4

reply to post by GypsK


I'm pretty sure the correct and only answer is -4

1 - 3 x 4 + 7 =

1 - 12 + 7 =

1 + (-12) + 7 = -4


If you do it this way...it doesn't matter if you do "1 + (-12)" first or "(-12) + 7" first...you will still get -4.

(1 + (-12)) + 7 = -11 + 7 = -4

1 + ((-12) + 7) = 1 + (-5) = -4

It's one of those tricky problems where order of operations can mess you up...long story short...think of subtraction as the sum of a negative number.

okok.... not to mention that my kid is learning this in school as we speak, lol


you think I'm stupid?
do this calculation on a calculator then! (seriously, do it)

It all depends on how you arrange the question I think. If you try to do it without applying any parenthesis (brackets) I think it gets a bit more complex, you need to understand the order of operations. However, I'm getting confused. When the equation is typed in as is (into a scientific calculator), I get -12. But the order of operations is Multiplication, Division, Addition, Subtraction as far as I know. Meaning the equation should be processed as follows:

1-((4x5)+7)

I think? But that gives me -26, it seems my calculator is interpreting it as:

(1-(4x5))+7

I dunno...mathematics gets too complicated at points...it's the simple things that can cause the biggest problems...

reply to post by Numino

1-(3x4)+7 = 1-12+7 = -4

But wouldn't you then group 12 and 7, because you do addition before subtraction? Like: 1-(12+7) = -18

reply to post by GypsK


you're supposed to do multiplication and division before addition and subtraction

reply to post by GypsK


My calculater says -1, but you can´t trust that.
You have to multiply or/and divide first before you add or/and use subtraction.

1. Multiplication & Division then 2. Addition & Subtraction

reply to post by BobbinHood


that's what I did
1-3x4+7
1-12+7
1-19
-18

Originally posted by CHA0S
reply to post by Numino

 

1-(3x4)+7 = 1-12+7 = -4

But wouldn't you then group 12 and 7, because you do addition before subtraction? Like: 1-(12+7) = -18

You don't do addition before subtraction...that is the problem. You do them "at the same time"...lol.

Because subtraction is just the addition of a negative number.

So: 10 - 5 can be written as 10 + (-5)

So: 1 - 12 + 7 is written as 1 + (-12) + 7.

Then like I said before...doesn't matte which you add first...the answer is -4.

Numbers make Heff angry. You wouldn't like Heff when he's angry.

Heff CRUSH numbers!!!!!

No, really, my vote is for -4 too, but I am horrible at math. (Elegant language my posterior!)

~Heff

reply to post by OutKast Searcher

So: 10 - 5 can be written as 10 + (-5)

So: 1 - 12 + 7 is written as 1 + (-12) + 7.

Of course, good explanation, so that proves my scientific calculator sucks. I always thought they were meant to be able to handle a simple equation like that without needing brackets?

reply to post by GypsK


I don't think you are stupid...I think it is a tricky math problem.

I don't doubt many calculators would get this wrong, because they use the strict definition of order of operations doing addition before subtraction.

When in reality, it should do subtraction as the sum of a negative...it's an error in the calculators software.

I would guess some really bad calculators would do it like this:

1 - 3 x 4 + 7 = (1 - 3) x 4 + 7 = (-2 x 4) + 7 = -8 + 7 = -1

In that case the calculator is simply doing left to right calculations...which is wrong.

reply to post by OutKast Searcher


I didn't think you think me stupid, just thought myself stupid for having trouble with pre-school math (so to speak)

but ok... as it slowly starts coming back

you said:
1+(-12)+7... doesnt matter which you do first, the answer is -4
but...shouldn't that be
1-(+12)+7.... and then I still don't know which one to do first and then it could be -4 or -18

and in all honesty, I did a google search on this one, posted in may forums but never with the right answer, just a lot of discussion. (not that I don't believe you)

reply to post by GypsK

but...shouldn't that be
1-(+12)+7.... and then I still don't know which one to do first and then it could be -4 or -18

WTF?!?!?! I give up...

2nd

reply to post by CHA0S


lol you know what? I give up as well
I'm sure the OP will jump in here shortly with an explaining post revealing the right method to solve this... or he lets this continue for a while....

it could be -4, not saying that the other posters are incorrect

This is always a great joke to play on people. because they sit around for hours trying to figure this one out.
The answer is -4.
However due to PEMDAS you get a bit confused.

The trick is to do addition and subraction from left to right.

reply to post by grey580


heh, I would've let everyone soak in it for a couple more days! lol

but thanks