# Maths... they do still teach it in schools, right?

• I'm on facebook, checking how many awesome friends I have when I see this:

6 - 1 x 0 + 2 / 2

"Challenge Accepted" I think to myself. I do mention that it depends on the order of precedence - but the correct answer taking that into account is 5.

Several thousand people have answered, some of them citing the above 'rules' - but a lot of people are coming to a conclusion of 7

SEVEN....?

I asked how anyone had got to 7 and some guy came out with some bullshit about the subtract sign inverting the 1 making it 6 + ((-1 x 0) + (2 / 2))... how exactly the fuck does that work?

Do I need to go on a bell tower climbing killing spree with a sniper rifle or are people just making this maths shit up on the fly? Tomorrow I expect to walk into a shop, spend £9.35, give the cashier £10 and get 7p change because they just decided to add some their own bullshit rules or maybe they are just counting in base 11.5...

Then I realise its 7

• The minus sign doesn't matter. 6 + 0 is the same as 6 - 0.

• BEDMAS:

1. Brackets
2. Exponents
3. Division, Multiplication

= 6 - 1 x 0 + 2 / 2

= 6 - (1 x 0) + (2 / 2)

= 6 - (0) + (1)

= 6 + 1

= 7

Where did 5 come from?

• Well, I ended up doing it right to left and forgetting about the minus/plus precedence - then I headdesked.

• @Charleh said:

or are people just making this maths shit up on the fly?

Only the imaginary numbers.

• @Charleh said:

I'm on facebook, checking how many awesome friends I have when I see this:

6 - 1 x 0 + 2 / 2

"Challenge Accepted" I think to myself. I do mention that it depends on the order of precedence - but the correct answer taking that into account is 5.

Several thousand people have answered, some of them citing the above 'rules' - but a lot of people are coming to a conclusion of 7

SEVEN....?

I asked how anyone had got to 7 and some guy came out with some bullshit about the subtract sign inverting the 1 making it 6 + ((-1 x 0) + (2 / 2))... how exactly the fuck does that work?

Do I need to go on a bell tower climbing killing spree with a sniper rifle or are people just making this maths shit up on the fly? Tomorrow I expect to walk into a shop, spend £9.35, give the cashier £10 and get 7p change because they just decided to add some their own bullshit rules or maybe they are just counting in base 11.5...

Then I realise its 7

*Complains about people not knowing maths.

*Doesn't know maths.

• @Master Chief said:

@Charleh said:

I'm on facebook, checking how many awesome friends I have when I see this:

6 - 1 x 0 + 2 / 2

"Challenge Accepted" I think to myself. I do mention that it depends on the order of precedence - but the correct answer taking that into account is 5.

Several thousand people have answered, some of them citing the above 'rules' - but a lot of people are coming to a conclusion of 7

SEVEN....?

I asked how anyone had got to 7 and some guy came out with some bullshit about the subtract sign inverting the 1 making it 6 + ((-1 x 0) + (2 / 2))... how exactly the fuck does that work?

Do I need to go on a bell tower climbing killing spree with a sniper rifle or are people just making this maths shit up on the fly? Tomorrow I expect to walk into a shop, spend £9.35, give the cashier £10 and get 7p change because they just decided to add some their own bullshit rules or maybe they are just counting in base 11.5...

Then I realise its 7

*Complains about people not knowing maths.

*Doesn't know maths.

• BODMAS, as my maths teacher used to say..

[B]rackets (parantheses, actually, but it sounds better than PODMAS)
[O]f (aka "multiply")
[D]ivision
M]ultiplication
[A]ddition
[S]ubtraction

• @Quango said:

BODMAS, as my maths teacher used to say..

[B]rackets (parantheses, actually, but it sounds better than PODMAS)
[O]f (aka "multiply")
[D]ivision
M]ultiplication
[A]ddition
[S]ubtraction

PEMDAS in these parts. Parentheses, exponents, multiplication/division, addition/subtraction. I swear my sixth grade teacher turned it into a song that we had to sing for a grade.

• @Quango said:

BODMAS, as my maths teacher used to say..

[B]rackets (parantheses, actually, but it sounds better than PODMAS)

[O]f (aka "multiply")

[D]ivision

M]ultiplication

[A]ddition

[S]ubtraction

Your Maths teacher was somewhat incorrect; or you're misremembering - the O stands for Orders (exponents and roots).

• @Master Chief said:

*Complains about people not knowing maths.

*Doesn't know maths.

THAT is the joke!

• Fucking Maths: How do They Work?

Every time I start thinking that the posters to TDWTF or slashdot are freaking boneheads, I just go over and read a couple Facebook or Yahoo threads. Then I realize what true microcraniality is.

• Minus is right-associative, riiiiiiiiight?

• Don't feed the trolls. It's deliberately intended to be ambiguous, so you'll comment on it. They are trolling for comments and likes. Accounts with a lot of comments and likes are valuable to advertisers.

• @GoatRider said:

Don't feed the trolls. It's deliberately intended to be ambiguous, so you'll comment on it. They are trolling for comments and likes. Accounts with a lot of comments and likes are valuable to advertisers.

What? No it's not, it's perfectly clear.

This one is deliberately ambiguous: a/b(c+d)

Because written as a/b*(c+d) the left to right rule gives this order of evaluation: (a/b)(c+d).
But the ommited multiplication sign creates ambiguity because that's usually only done in situations where you would have this order of evaluation: a/(b
(c+d)), the same way as writing it out as a fraction gives you implicit parentheses:

a

-------------

b*(c+d)

• I was just reading the Excel woes sheet - and it kind of crosses with this thread:

Type this into Excel and be angry:

Cell A1: =-5

Cell A2: =-a1^2+1

Cell A3: =+1-a1^2

You can actually find the history behind this !!fun!! with a search, but it's still irritating.  I don't know how many spreadsheets have given me funny results because of this "design choice."

I was just reading the Excel woes sheet - and it kind of crosses with this thread:

Type this into Excel and be angry:

Cell A1: =-5

Cell A2: =-a1^2+1

Cell A3: =+1-a1^2

You can actually find the history behind this !!fun!! with a search, but it's still irritating.  I don't know how many spreadsheets have given me funny results because of this "design choice."

Am I missing something?

-a1^2+1 = 5^2+1 = 25 + 1 = 26

+1-a1^2 = +1 - (-5)^2 = +1 - 25 = -24

Which is exactly the result I get from Excel...

Cell A1: =-5

Cell A2: =-a1^2+1

Cell A3: =+1-a1^2

A2 has the value of (-5) raised to the second power, with one added to the result.

Do you want it to have the value of (-5) raised to the third power?  If so, you need parentheses!

• @joe.edwards said:

Am I missing something?

-a1^2+1 = 5^2+1 = 25 + 1 = 26

+1-a1^2 = +1 - (-5)^2 = +1 - 25 = -24

Which is exactly the result I get from Excel...

The question is on the precedence on the - sign in front of the A1. Either you write

-a1^2+1 = -(-5)^2+1 = 25 + 1 = -24

+1-a1^2 = +1 - (-5)^2 = +1 - 25 = -24
or by using the rule that "-A1" is exactly the same as "+ ( -1 * A1 ):

-a1^2+1 = (-1 * -5)^2+1 = 25 + 1 = 26

+1-a1^2 = +1 + (-1 * -5)^2 = +1 - 25 = 26
The second one, giving 26, seems wrong. Taking the power of 2 of A1 should have precedence over applying the minus sign

• I think the point is that the minus sign in A2 is being treated differently than in A3. Eg, in A2, it has higher priority than the exponent:

-a1)^2+1

=-(a1^2)+1

Whereas in A3, the minus sign is the subtraction operator, and has a lower priority than the exponent. If you rewrite A2 like this, it matches A3:

=0-a1^2+1

I guess they added logic to handle minus signs in places where subtraction doesn't make sense, like the beginning of the formula, or this:

=5 +- a1

• TRWTF is British English. If it's really "maths", it should be "they do still teach THEM in schools, right?"

• I guess I see it that - can be a unary operator or a binary operator, and that as a unary operator it yields the additive inverse of the number and has immediate precedence, while as a binary operator it has lesser precedence. In any case, it's acting in line with my expectations. -x is evaluated as (-1x).

• @Charleh said:

Well, I ended up doing it right to left and forgetting about the minus/plus precedence - then I headdesked.

In that case you should get 1, not 5.

• @pkmnfrk said:

BEDMAS:

1. Brackets
2. Exponents
3. Division, Multiplication

= 6 - 1 x 0 + 2 / 2

= 6 - (1 x 0) + (2 / 2)

= 6 - (0) + (1)

= 6 + 1

= 7

Where did 5 come from?

Congratulations. You are the 100,000 person who didn't read the whole story. You have won an Internet!

• @TGV said:

Congratulations. You are the 100,000 person who didn't read the whole story. You have won an Internet!

Is that the one-hundred thousandth person, or the one hundredth to a precision of one thousandth?

(Yes, this is intentional).

•  It's the 100'000th person.

• @ekolis said:

TRWTF is British English. If it's really "maths", it should be "they do still teach THEM in schools, right?"
And if it's British English, right? should be innit?

• @TGV said:

@pkmnfrk said:

BEDMAS:

1. Brackets
2. Exponents
3. Division, Multiplication

= 6 - 1 x 0 + 2 / 2

= 6 - (1 x 0) + (2 / 2)

= 6 - (0) + (1)

= 6 + 1

= 7

Where did 5 come from?

Congratulations. You are the 100,000 person who didn't read the whole story. You have won an Internet!

I was calling into attention a bit of the story that you clearly did not read:

@Charleh said:

but the correct answer taking that into account is 5.

• My guess...

@pkmnfrk said:

I was calling into attention a bit of the story that you clearly did not read:

@Charleh said:

but the correct answer taking that into account is 5.

= 6 - 1 x 0 + 2 / 2

= 6 - (1 x 0) + (2 / 2)

= 6 - (0 + 1)

= 6 - (1 x 0) + (2 / 2)

= 6 - (0 + 1)

But clearly wrong, because those two aren't equivalent, since you're introducing a multiplication in the second one.

• @pkmnfrk said:

BEDMAS:

1. Brackets
2. Exponents
3. Division, Multiplication

= 6 - 1 x 0 + 2 / 2

= 6 - (1 x 0) + (2 / 2)

= 6 - (0) + (1)

= 6 + 1

= 7

Where did 5 come from?

5 comes from inserting an invisible parentheses that don't belong, opening either before the 1 or the 0 and ending at the end of the statement.

Solving in reverse-polish notation you get:

6 (push), 1 (push), 0 (push),  (multiply), (subtract), 2 (push), 2 (push), (divide), (add)

Each operation either pushes a number onto the stack or performs a binary operation between the 2 most recent numbers on the stack.

A subtract subtracts the current value from the one before it on the stack.

An operation replaces the last 2 numbers on the stack with the value of the current one.

Stack looks like this:

(push 6) 6

(push 1) 6, 1

(push 0) 6, 1, 0

(multiply) 6, 0

(subtract) 6

(push 2 ) 6, 2

(push 2) 6, 2, 2

(divide) 6, 1

• Mr CButtius! Will the test be graded on a curve? I did bad on the quiz because my dog was barking and kept me up but I need a C on the test or I won't be able to go to prom!!!

God you people are boring.

•  I bring worlds together.

• There, now I got SOME enjoyment out of this thread.

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