1-3x4+7=?

Originally posted by grey580
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.

Or just change it into an addition problem...which is what subtraction really is anyway.

Then the order doesn't matter.

The "doing it from left to right" isn't really a solid math rule or law...it's more of just a trick for people to remember to get the correct answer.

That's why I prefer to turn it into addition and apply the Cumulative Property.

Originally posted by grey580
1-3x4+7=?
Discuss.

-4

- Phoenix

I haven't had math in50 years I came up with -15 never was the brightest crayon in the box.

reply to post by grey580


1-3x4+7=?

PEMDAS

parenthesis, exponents, multiplication, division, addition, subtraction

3*4= 12
12 + 7=19
1-19= -18

odds are i'm probably doing something wrong. this thread might be the most frightening (for exposing my own ignorance) that i've ever encountered

reply to post by OutKast Searcher



oh snap. i've been had by 3rd grade math!

All you have to do is type 1-3x4+7 in on your calculator and you get -4

That is the right answer.

Well this depends on the order you would operate.

Normally someone would come up with -4

I do know some who would also get -5

1-3x4+7
1(-3x4)+7
1(-12)+7
-5

Just saying that it depends on how you remember math being taught. How you remember things.

There is a right way and a wrong way. Ill leave it with you to ponder that.

1-3x4+7
-2x11=-22



Being odd is better than being right.

ANSWER IS -22. SUNBURN did it right basic math lol, my math teacher try to play us with a question like this on a test (2nd year of college)

Originally posted by ^anubis^
ANSWER IS -22. SUNBURN did it right basic math lol, my math teacher try to play us with a question like this on a test (2nd year of college)

edit on 13-10-2010 by ^anubis^ because: (no reason given)

I'm not sure what college you went to...but I'd get my money back.

The answer is -4...it is basic math...it is NOT -22.

it is just 18.

Hello Everyone. I can't believe it took a math problem to make me post a reply after only viewing ATS for 2 years. ^^

Anyway, I cheated and typed this problem into Excel to see if it agreed with the answer of -4 and it certainly did. No brackets or parentheses were needed. Also, just for lolz, I typed the problem into my antiquated motorola razr cellphone and it gave me the same answer of -4. Strangely though, I opened windows calculator (calc.exe) and tried this problem in standard mode and scientific mod and received 2 different answers. Standard mode give -1 as the answer while scientific mode gives -4 as the answer.

The answer is -4. You do addition left to right. You wouldn't do 12 + 7 = 19 then subtract from 1. That would be right to left. We just want to subtract the 12 from 1. We don't want to subtract the 12 plus subtract 7 more. We want to add 7 more. You would subtract 12 from 1 first which would be -11 and then add the 7 which equals -4.

As long as you're using + and - as instructions, the instructions must be carried out in order. If you want to do it commutatively and move the numbers around then you have to make sure you're moving the number's SIGN with it as well.

The positive + sign symbols on numbers are usually missing. Only when it's negative do you put the -. So, people start thinking + and - are instructions and that + means to add and - means to subtract, but they're not instructions. They're supposed to be used as labels. They tell you what the number's sign is.

Don't get tricked by it though. Just put the missing sign symbols back in yourself and all becomes clear. For every number that doesn't have an - next to it, just put a + next to it.

+1, -3, +4, +7. When you do math this way you NEVER subtract. You multiply the numbers first, and then add up the remaining terms, but you'll be adding negative numbers so you get the same results. Plus and minus signs are no longer instructions for you to do something, but now have been turned into labels that tell you what each number's sign is. So, the equation you actually have is this.

+1 plus -3 times +4 plus +7.

Multiplication first. -3 x +4 = negative 12.

This is where some are getting tripped up. By saying +12 + 7 = 19. But that's wrong! THERE IS NO +12! The 12 we have is a -12, not a +12. We got -12 from multiplying a NEGATIVE 3 times a positive 4. The correct answer here is -12 + 7 = -5 and not 19.

So now you have a positive 1 and a negative 5. You can ADD the -5 to +1 and you'll get -4. The correct answer.

This is actually the right way to do addition because there is no such thing as subtraction. Doesn't exist! Only addition exists. You always just add up all the numbers. Subtraction is just the addition of the negative numbers. Anytime you see an - sign don't say minus to yourself. Say plus negative so you know which number the - belongs to. 1 - 3 is 1 plus negative 3.

i dunno how people get all these answers - there are only two credible soltions -

the firsts - a literal approach gives -1 this SEEMS correct

ie :

1-3 = -2

-2 * 4 = -8

-8 + 7 = -1

the second - actually correct answer gives -4 as this follows the rulles of mathematical equations , which are counterintuitive

reply to post by ignorant_ape


You have to do the multiplication first. You can't do 1 - 3 = -2 and then times the -2 by 4 because there is no 3, and if there's no 3 then there's no -2.

A 3 is the same thing as saying 3 number ones. Saying 4 is the same thing as saying 4 number ones. It's just the 1 is implied. So 1 - 3 is the same thing as writing 1 - 1 - 1 - 1 because you have to subtract 1 from 1 three times.

Remember what multiplication is. It's how many you have of the other number. 5 x 5 means I have 5 number fives. 3 x 8 means I have 3 number eights. It doesn't mean I have 3. It means I have 3 number eights which is a different number than just three. So for example 3 x 4 is 3 number fours. You could also right it like this, 4 + 4 + 4.

So when you do 1 - 3 first it's not correct because there is no 3. You have three fours, not three ones. You would have to subtract 4, but you would have to do it 3 times because you have 3 number fours. You'd have to do 1 - 4 - 4 - 4 + 7 because you have to subtract all three of your fours or all four of your threes if you prefer it the other way around.

Doing the multiplication first is just an easy way of skipping this step. You can just multiply it up into one big number and add and subtract all your 4s at once.

3 number fours is 12 because 4 + 4 + 4=12. 1 - 12 (subtracting all fours at once) = -11 then + 7 = -4.

Hello new here but thought i had to reply on this one as in in class right now having math.

1-3x4+7=-4

the way it should be calculated is like this

1+(-3)x4+7

which gives

1+(-12)+7

then i should be obvious from there

reply to post by tinfoilman


thanks for that, you explain it in a way most mathteachers can't explain!
I'm sure my math teacher didn't!

I understand completely now and when my daughter starts having trouble with these I'm sure I'll be able to explain it to her

This is how you solve the equation:

- 3 x 4 + 1 + 7

Why?

Because what you see is this: +1.......-3x4.......+7

You first have to find out what -3x4 is.

-3x4 is -12.

than you get -12 +1 +7 = -4

Really Guys?

1-(3x4)+7=-18

3x4=12

1-12+7=

12+7=19

1-19= -18

Problem Solved.

Originally posted by Lothrigen
Really Guys?

1-(3x4)+7=-18

3x4=12

1-12+7=

12+7=19

1-19= -18

Problem Solved.

You can't add brackets like you did. You just created a different equation that is not even like the original equation.

This is what the original equation really is: +1-3x4+7

All you have to do is space out the equation and it becomes as clear as day how your supposed to solve it.

+1......-3x4.......+7

If you write it as a sentence it will read: Positive One, negative 3 times four, plus seven.