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

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pete75
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby pete75 » 16 Mar 2016, 1:45am

[XAP]Bob wrote:Equally valid to say that there are three front left legs, 3 front right etc...

Makes more sense to do so when number of dogs > number of legs per dog


Not really. Anyhow to put it another way 5*3 = 3+3+3+3+3 3*5 =5+5+5

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[XAP]Bob
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby [XAP]Bob » 16 Mar 2016, 6:05am

pete75 wrote:
[XAP]Bob wrote:Equally valid to say that there are three front left legs, 3 front right etc...

Makes more sense to do so when number of dogs > number of legs per dog


Not really. Anyhow to put it another way 5*3 = 3+3+3+3+3 3*5 =5+5+5


Now do that for 100 dogs.

Which is more sensible:
100+100+100+100 or
4+4+4+4+4+.........

When one number is larger than the other it makes sense to use that number as the base for addition.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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[XAP]Bob
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby [XAP]Bob » 16 Mar 2016, 6:12am

The two images are not single photos, they are composites - one is mostly from 700km, is centred on the gulf and imaged between May and September are combined with ground based observations and various other data sources.

The other is centred significantly south west of the gulf, and uses a number of images taken on one day by a different satellite, at different actual altitude, certainly using a different camera. It's also got a radically different perspective altitude (i.e. where the images are stitched together from)



Oh look:
http://www.nasa.gov/sites/default/files/thumbnails/image/viirs_9apr2015.jpg

The Gulf of Mexico has disappeared completely!

Amaze balls, it's all fake!!!!?!!1!!!

Edit - That's not a thumbnail NASA...
Sorry if I broke your browser


Just taken two photos of the same bottle:
BottlePerspective.JPG


Note how the words span the whole bottle on one image and not on the other....
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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

Postby drossall » 16 Mar 2016, 8:05am

Manc33 wrote:I have never mentioned "outside observers". That has been introduced into it from nowhere for no reason, a red herring, a complication.

You're right, of course; I woke up this morning realising that the analogy didn't work. I must be getting old.

But I do think that you are arguing that the air doesn't exist, because you don't feel the pressure of it on your skin.

pete75
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby pete75 » 16 Mar 2016, 8:13am

[XAP]Bob wrote:
pete75 wrote:
[XAP]Bob wrote:Equally valid to say that there are three front left legs, 3 front right etc...

Makes more sense to do so when number of dogs > number of legs per dog


Not really. Anyhow to put it another way 5*3 = 3+3+3+3+3 3*5 =5+5+5


Now do that for 100 dogs.

Which is more sensible:
100+100+100+100 or
4+4+4+4+4+.........

When one number is larger than the other it makes sense to use that number as the base for addition.


It may well be but doesn't follow the rules of repeated addition which is what the person who set the question wanted to see demonstrated, Personally I think it's a pretty pointless exercise presumably invented to teach something about numbers or sets of numbers.

In my day we had similar silly questions like water is running into a bath from a tap at 1 gallon minute a minute and out of the plug hole at 1/2 a gallon a minute. It holds 20 gallons. How long will it take to fill. Correct answer 40 minutes sensible answer put the plug in and it will take 20.
The first rule of answering exam type questions is give the examiner what they want.

pete75
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby pete75 » 16 Mar 2016, 8:13am

drossall wrote:
Manc33 wrote:I have never mentioned "outside observers". That has been introduced into it from nowhere for no reason, a red herring, a complication.

You're right, of course; I woke up this morning realising that the analogy didn't work. I must be getting old.

But I do think that you are arguing that the air doesn't exist, because you don't feel the pressure of it on your skin.

Maybe he spends his life in a vacuum.

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[XAP]Bob
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby [XAP]Bob » 16 Mar 2016, 8:17am

pete75 wrote:
[XAP]Bob wrote:
Now do that for 100 dogs.

Which is more sensible:
100+100+100+100 or
4+4+4+4+4+.........

When one number is larger than the other it makes sense to use that number as the base for addition.


It may well be but doesn't follow the rules of repeated addition which is what the person who set the question wanted to see demonstrated, Personally I think it's a pretty pointless exercise presumably invented to teach something about numbers or sets of numbers.

In my day we had similar silly questions like water is running into a bath from a tap at 1 gallon minute a minute and out of the plug hole at 1/2 a gallon a minute. It holds 20 gallons. How long will it take to fill. Correct answer 40 minutes sensible answer put the plug in and it will take 20.
The first rule of answering exam type questions is give the examiner what they want.


The student did - they solved the correct multiplication problem, using the method prescribed (which is in itself a bad question).
The fact that the examiner is an idiot shouldn't affect the student's grade.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

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

Postby profpointy » 16 Mar 2016, 8:50am

Bearing in mind "the repeated addition method" is not a formal mathematical definition but a learning aid. 5x3 is a mathematical statement and Ibl believe it is simply wrong to contend that it means 5 lots of 3 rather than lots of 5, 3 times. I tcould just about be defensible if the question had been stated as 5 lots of 3 things and then go on to show multiplication (of numbers) is commutative. a x b has no ordering. The question is bad, and the student's answer is correct according to the question. For what it's worth I have a maths degree (albeit a poor one)

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

Postby beardy » 16 Mar 2016, 9:31am

The difference is that the question isnt really a maths question but a question about a teaching method and to see if the pupil has grasped the concept about the teaching method.

A case of the "teaching and assessment" tail wagging the education dog.

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

Postby Audax67 » 16 Mar 2016, 9:35am

Myself when young did eagerly frequent
Doctor and Saint, and heard great Argument
About it and about: but evermore
Came out by the same Door as in I went.

- Omar Khayyam


You sages have just repeated most of the content of the first page of the topic.

I suppose we may be thankful that conversation hasn't degenerated into a discussion of contraflow cycle-lane systems as applied to 2-way roundabouts. ;)
Have we got time for another cuppa?

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

Postby profpointy » 16 Mar 2016, 9:37am

beardy wrote:The difference is that the question isnt really a maths question but a question about a teaching method and to see if the pupil has grasped the concept about the teaching method.

A case of the "teaching and assessment" tail wagging the education dog.


Quite! And even worse, testing whether the pupil can remember the order taught in class of 5x3 versus 3x5 even though no mathematician who hadn't been to the class could answer that with certaintiy

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

Postby sjs » 16 Mar 2016, 1:32pm

beardy wrote:The difference is that the question isnt really a maths question but a question about a teaching method and to see if the pupil has grasped the concept about the teaching method.

A case of the "teaching and assessment" tail wagging the education dog.

Exactly

pete75
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Re: Any Maths Genius To Explain why "5+5+5=15 is incorrect"

Postby pete75 » 16 Mar 2016, 2:14pm

[XAP]Bob wrote:
The student did - they solved the correct multiplication problem, using the method prescribed (which is in itself a bad question).
The fact that the examiner is an idiot shouldn't affect the student's grade.


As I said the first rule of exam success is to give the examiner what they want. BTW I very much doubt this was a question given to a student - primary school pupil is my guess.

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

Postby Psamathe » 16 Mar 2016, 2:18pm

pete75 wrote:
[XAP]Bob wrote:
The student did - they solved the correct multiplication problem, using the method prescribed (which is in itself a bad question).
The fact that the examiner is an idiot shouldn't affect the student's grade.


As I said the first rule of exam success is to give the examiner what they want. BTW I very much doubt this was a question given to a student - primary school pupil is my guess.

Given to US Third Grade student (8-9 years old ?). No idea where this fits in terms of "primary school".

Ian

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

Postby Mick F » 16 Mar 2016, 2:50pm

Audax67 wrote:I suppose we may be thankful that conversation hasn't degenerated into a discussion of contraflow cycle-lane systems as applied to 2-way roundabouts. ;)
......................... What's wrong with contraflow cycle-lane systems as applied to 2-way roundabouts?

What's a 2-way roundabout anyway?
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