Any Maths Genius To Explain why "5+5+5=15 is incorrect"

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Psamathe
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Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby Psamathe » 28 Oct 2015, 5:45pm

I saw the headline "Parents criticise US Common Core maths after third grade pupil told solution for 5+5+5=15 is incorrect" but BT engineer was here and I had no broadband so could not understand why. Later I read the article and seems the question was "Use the repeated addition strategy to solve 5 x 3 = ". The student did 5+5+5=15 and was marked wrong because the correct answer was 3+3+3+3+3=15.

And I still can't understand what the student did wrong.

Article (no paywalls) http://www.independent.co.uk/student/news/parents-criticise-us-common-core-maths-after-third-grade-pupil-told-solution-for-55515-is-incorrect-a6711736.html

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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby Audax67 » 28 Oct 2015, 6:00pm

It looks as if the "repeated addition strategy" (God wot) is more like an algorithm that says "write out the second number as many times as the value of the first number".

Whoever invented it should be required to solve 1,000,000 x 3, and should not be fed, watered or taken for walkies until they've done it.

And then they should be compelled to use their matricidal version on the same "problem".

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Psamathe
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby Psamathe » 28 Oct 2015, 6:08pm

(With my limited maths ability, and not having ever been a teacher) I would have given the student additional marks for simplifying the problem - shows thinking "outside the box" to make the problem easier.

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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby [XAP]Bob » 28 Oct 2015, 7:10pm

The student should not have been marked wrong, multiplication and addition are both commutative.

The marking scheme was incomplete, and the teacher should have spotted that and reported the omission to the relevant people to issue an amendment...
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby TonyR » 28 Oct 2015, 7:35pm

I think it was marked right. The question is write out additively fives times three i.e. three five times.

Of course it could have been an accountancy exam in which case the correct answer to what is five times three is "What would you like it to be?" :wink:

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Re: Any Maths Genius To Explain why

Postby Psamathe » 28 Oct 2015, 7:52pm

TonyR wrote:I think it was marked right. The question is write out additively fives times three i.e. three five times.
...

I took the question to say what strategy (which I interpret as "technique" or method) to solve a multiplication question. To me, no specification about how it should be written out, just the method/technique to solve the equation.

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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby Mark1978 » 28 Oct 2015, 7:56pm

Everything comes down to addition. That's how computers work. They can't divide, multiply or subtract, only add.

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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby TonyR » 28 Oct 2015, 8:18pm

Psamathe wrote:
TonyR wrote:I think it was marked right. The question is write out additively fives times three i.e. three five times.
...

I took the question to say what strategy (which I interpret as "technique" or method) to solve a multiplication question. To me, no specification about how it should be written out, just the method/technique to solve the equation.

Ian


It doesn't ask which strategy, its says to use a particular strategy to solve three, five times, not five, three times

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Re: Any Maths Genius To Explain why

Postby Psamathe » 28 Oct 2015, 8:25pm

TonyR wrote:
Psamathe wrote:
TonyR wrote:I think it was marked right. The question is write out additively fives times three i.e. three five times.
...

I took the question to say what strategy (which I interpret as "technique" or method) to solve a multiplication question. To me, no specification about how it should be written out, just the method/technique to solve the equation.

Ian


It doesn't ask which strategy, its says to use a particular strategy to solve three, five times, not five, three times

This is where we are reading it differently as I'm reading it as the student is being told the technique to use to solve an equation. i.e they are giving yo an equation to find the answer to and telling you the technique to use (how I read it).

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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby Geoff.D » 28 Oct 2015, 8:33pm

This might well be a victory for the jobsworths on the curriculum board. If they have ordained that (a) third grade students, about 8 years old, will not yet have been introduced to the concept of commutation, and (b) the definition of the "repeated addition strategy" is always "the first number of additions of the second" then the student has gone outside the bounds of being correct. Quite rebellious, in fact.

He she certainly doesn't deserve any reward for being ahead of the curriculum or finding a more elegant solution. Nor does he/she deserve any credit for having his/her own independent mathematical thoughts.

I remember taking the theory part of a driving test in USA in the 70's. It was multiple choice. Having finished the test I took it to an official, who put a template over the sheet. The template had holes where the correct answers would show. I was told I had scored zero. Looking over the desk, I asked the officer to put the template the right way up and, lo and behold, I passed. Sadly, jobsworths (either in person or systematised) aren't able to discriminate.

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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby 661-Pete » 28 Oct 2015, 9:55pm

I'd just love to see that poor misbegotten teacher have a matrix multiplication thrown at him/her!

Code: Select all

(5 6)  x  (3 4)    anyone?
(7 8)     (5 6)

and then, just for fun,
(3 4)  x  (5 6)
(5 6)     (7 8)
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby Mick F » 29 Oct 2015, 9:19am

We did matrix sums at school in the mid 60's.
We didn't use double brackets like that, but one big bracket either side of the groups. It looks wrong the way you've done it, but maybe that's the only way a word processor can do it.
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby 661-Pete » 29 Oct 2015, 9:29am

If you know of a way of posting double-height brackets on this forum, let us know! I did the best I could...
Next test: post an integral sign.....
Suppose that this room is a lift. The support breaks and down we go with ever-increasing velocity.
Let us pass the time by performing physical experiments...
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby gaz » 29 Oct 2015, 9:42am

∫ ... I did the best I could :wink: .
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby 661-Pete » 29 Oct 2015, 10:51am

gaz wrote:∫ ... I did the best I could :wink: .

I should have known Unicode would have something. OK then:

What about a definite integral then? With user-defined limits.
Suppose that this room is a lift. The support breaks and down we go with ever-increasing velocity.
Let us pass the time by performing physical experiments...
--- Arthur Eddington (creator of the Eddington Number).