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

[pete75]

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

[[XAP]Bob]

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.

[[XAP]Bob]

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:

Note how the words span the whole bottle on one image and not on the other....

[drossall]

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]

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]

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.

[[XAP]Bob]

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.

[profpointy]

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]

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.

[Audax67]

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.

[profpointy]

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

[sjs]

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]

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.

[Psamathe]

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

[Mick F]

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?