Maths brainteaser.

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bindeweede
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Maths brainteaser.

Post by bindeweede » Mon Nov 02, 2015 6:44 pm

Found on Facebook.
5 + 5 + 5 - 5 + 5 + 5 - 5 + 5 x 0 = ?
The answer hasn't been posted, but I know I got it wrong. And I know why. I should have remembered that course I did in 1986.

panama
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Re: Maths brainteaser.

Post by panama » Mon Nov 02, 2015 6:45 pm

bindeweede wrote:Found on Facebook.
5 + 5 + 5 - 5 + 5 + 5 - 5 + 5 x 0 = ?
The answer hasn't been posted, but I know I got it wrong. And I know why. I should have remembered that course I did in 1986.

I would think there are number of possible answers depending on how you group the operations...however that x0 at the end suggests that the answer will be 0...if I've remembered the conventions correctly.

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Re: Maths brainteaser.

Post by bindeweede » Mon Nov 02, 2015 6:46 pm

panama wrote:
bindeweede wrote:Found on Facebook.
5 + 5 + 5 - 5 + 5 + 5 - 5 + 5 x 0 = ?
The answer hasn't been posted, but I know I got it wrong. And I know why. I should have remembered that course I did in 1986.

I would think there are number of possible answers depending on how you group the operations...however that x0 at the end suggests that the answer will be 0...if I've remembered the conventions correctly.

Well, I answered 0, but then I remembered something about some operations having a sort of priority over others. I won't spoil it for now.

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Re: Maths brainteaser.

Post by chaggle » Mon Nov 02, 2015 6:47 pm

I'm pretty sure you do the multiplication first and then simply add up the rest making 10.
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Re: Maths brainteaser.

Post by bindeweede » Mon Nov 02, 2015 6:47 pm

Are you sure, chaggle? 56,000 people have what I think is the right answer, and it isn't 10 ;)

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Re: Maths brainteaser.

Post by DrS » Mon Nov 02, 2015 6:48 pm

I'd say 15 ... I made it 20 to begin with, but I think the final 5 is the only one (given that there aren't any brackets) that is multiplied by zero.

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Re: Maths brainteaser.

Post by chaggle » Mon Nov 02, 2015 6:49 pm

bindeweede wrote:Are you sure, chaggle? 56,000 people have what I think is the right answer, and it isn't 10 ;)
Sorry - I meant 15.
Don't blame me - I voted remain :con

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Re: Maths brainteaser.

Post by Silentecho » Mon Nov 02, 2015 6:49 pm

I would have said 0 too, unless it were written: 5 + 5 + 5 - 5 + 5 + 5 - 5 + [5 x 0] = 15

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Re: Maths brainteaser.

Post by Croydon13013 » Mon Nov 02, 2015 6:50 pm

Silentecho wrote:I would have said 0 too, unless it were written: 5 + 5 + 5 - 5 + 5 + 5 - 5 + [5 x 0] = 15
Yes. The way I was taught at school it is 0 unless you insert the brackets as you suggest.

I don't accept that 0 is wrong, only, perhaps, that there are different conventions for working it out that will give different answers.
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Re: Maths brainteaser.

Post by smudge » Mon Nov 02, 2015 6:50 pm

Croydon13013 wrote:
Silentecho wrote:I would have said 0 too, unless it were written: 5 + 5 + 5 - 5 + 5 + 5 - 5 + [5 x 0] = 15
Yes. The way I was taught at school it is 0 unless you insert the brackets as you suggest.

I don't accept that 0 is wrong, only, perhaps, that there are different conventions for working it out that will give different answers.

Ditto.

(Though I am notoriously crap at maths)

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Re: Maths brainteaser.

Post by panama » Mon Nov 02, 2015 6:51 pm

15 is the answer apparently. Here's a Wikipedia article on the subject http://en.wikipedia.org/wiki/Order_of_operations
n mathematics and computer programming, the order of operations (sometimes called operator precedence) is a rule used to clarify unambiguously which procedures should be performed first in a given mathematical expression.

For example, in mathematics and most computer languages multiplication is done before addition; in the expression 2 + 3 × 4, the answer is 14. Brackets, which have their own rules, may be used to avoid confusion, thus the preceding expression may also be rendered 2 + (3 × 4), but the brackets are not required as multiplication still has precedence without them.

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Re: Maths brainteaser.

Post by smudge » Mon Nov 02, 2015 6:52 pm

panama wrote:15 is the answer apparently. Here's a Wikipedia article on the subject http://en.wikipedia.org/wiki/Order_of_operations
n mathematics and computer programming, the order of operations (sometimes called operator precedence) is a rule used to clarify unambiguously which procedures should be performed first in a given mathematical expression.

For example, in mathematics and most computer languages multiplication is done before addition; in the expression 2 + 3 × 4, the answer is 14. Brackets, which have their own rules, may be used to avoid confusion, thus the preceding expression may also be rendered 2 + (3 × 4), but the brackets are not required as multiplication still has precedence without them.
Me being wrong about arithmetic would in no way be strange......

:(

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Re: Maths brainteaser.

Post by bindeweede » Mon Nov 02, 2015 6:52 pm

panama wrote:15 is the answer apparently. Here's a Wikipedia article on the subject http://en.wikipedia.org/wiki/Order_of_operations
If you use a simple calculator, the answer comes up as "0", but if you use something like a spreadsheet, which has all sorts of mathematical functions built in, it comes up with "15".

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Re: Maths brainteaser.

Post by Croydon13013 » Mon Nov 02, 2015 6:53 pm

bimbow wrote: If you use a simple calculator, the answer comes up as "0", but if you use something like a spreadsheet, which has all sorts of mathematical functions built in, it comes up with "15".
Yes.

So did the convention change at some point or are a number of us misremembering what we were taught?

The left to right method used by my calculator, and various of us, still seems more logical to me. Although when both Wikipedia and my Excel spreadsheet are ganging up on me I have to admit that I must be wrong.
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Re: Maths brainteaser.

Post by Brian1945 » Mon Nov 02, 2015 6:54 pm

The long-standing convention is X & / first, then + & -. Zero is wrong, the answer is definitely 15.

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