2 teachers telling DD different answers

[workshy]

DD year 5 got told she had missed a prime number out because she missed out number 1

she told the teacher that her other teacher had told her it wasn't a prime number because it only has 1 factor and the teacher told her she was wrong again

teacher that told her she was wrong was supply teacher, teacher that told her 1 isn't prime is the year 6 teacher

I know she is right, and she is 'really affronted by the injustice of it all' aparently

do I tell her to suck it up or does she argue her point? she has supply again tomorrow

print off some information from a reputable internet site and send dd in with it?

If it had been me at school I would have had to prove I was right to the person who was wrong before letting it lie.

en.wikipedia.org/wiki/Prime_number

Primality of one

Most early Greeks did not even consider 1 to be a number,[4] so did not consider it a prime. In the 19th century however, many mathematicians did consider the number 1 a prime. For example, Derrick Norman Lehmer's list of primes up to 10,006,721, reprinted as late as 1956,[5] started with 1 as its first prime.[6] Henri Lebesgue is said to be the last professional mathematician to call 1 prime.[7] Although a large body of mathematical work is also valid when calling 1 a prime, the above fundamental theorem of arithmetic does not hold as stated. For example, the number 15 can be factored as 3 · 5 or 1 · 3 · 5. If 1 were admitted as a prime, these two presentations would be considered different factorizations of 15 into prime numbers, so the statement of that theorem would have to be modified. Furthermore, the prime numbers have several properties that the number 1 lacks, such as the relationship of the number to its corresponding value of Euler's totient function or the sum of divisors function.[8][9]

But wikipedia is not necessarily reputable

(I have literally no idea how old children in year 5 are so this advice may be entirely inappropriate)

If she can argue her point without being rude she will never make it as a mumsnetter I see no reason for her to back down.

Do you have an encyclopaedia to hand? When you're right you're right. And she's right.

Whilst she is indeed correct, as it is a supply teacher and presumably they will have moved on from prime numbers in the next lesson I would tell her to adopt moral superiority, move on and forget about it.
If however, the lesson is still on primes and she gets asked again if 1 is a prime number, answer that it isn't and a google search will give the reasons(At least I am sure it will do, I haven't actually checked).

yr 5s are 9-10 yrs old, JGF

Like this

or this

I'm not sure whether arguing with the teacher is a good idea though. Would she be able to talk it over with the year 6 teacher who hopefully would set the supply teacher straight?

I am a mathematician. 1 is not prime. It is a unit. End of.

It's a tricky one! But I agree - she's right. I think I'd be unable to let it go. Could you print out the wiki article?

She could ask her supply teacher what the other factor of 1 is.

I'd be tempted to tell her to politely stick to her guns on this. She is right, but the outcome of that approach is so dependent on how she does it and how the supply teacher responds. I'd hate to think I'd encouraged her into trouble in anyway! With any luck, the supply has googled it this evening and found out her error.

I also happen to have written a dissertation on primality, so it's not as if I'm a fluid dynamicist offering my 2ps worth.

oh she won't let it go -she is like a dog with a bone if she knows she is right

I'll get her to have a chat with Yr6 teacher tomorrow, she usually has him on wednesdays :)

Prime numbers have exactly two factors. And so 1 is not a prime number.

She is right but I'm not sure whether she should push the point or not. Have a feeling my DS probably would push the point if the same situation happened to him but I'm not sure how tactful he would be...

Oh I'd missed that it was the year 6 teacher rather than her normal teacher who'd told her that 1 isn't a prime. Definitely agree that she should tell him then, and he can educate the supply teacher!

The approach isn't to ask what the other factor of one is. The key is unique factorisation - the integers (which we call Z) form a mathematical construct called a "ring" in which there is unique factorisation. This is called the fundamental theorem of arithmetic - stating that every non-zero integer can be written as the product of primes and the units (-1, 1). So for any given integer, there is a unique way of describing it in terms of its prime factors.

The ring of integers has to have units as part of its structure, and they're not primes (you can't write things uniquely as products of 1 and primes, as there could be many multiples of 1 involved.)

So your DD is right.

quip I'm going to memorise that lol

Thanks, scummy.

Good luck to your dd workshy! Speaking to the year 6 teacher seems like a really sensible plan.

But a way to think of it is....

Every number can be written in ONE way as 1 x Prime no (x prime no) (x prime no) etc etc

So 2 is 1 x 2
6 is 1 x 2 x 3

There are no other ways you can write them, so long as 1 isn't a prime.

If 1 was a prime, then you could say

2 = 1 x 1 x 2
Or
1 x 1 x 1 x 1 x 2

Which isn't allowed!

Is that clearer? Maybe not....

I actually found quip's explanation clearer lol

Lol!!

Quip I believe you..I got lost on line 1 but I have had the odd tonight....

The approach isn't to ask what the other factor of one is.
Well, it is if you happen to be in Year 5!

I would tell her sometimes teachers do get it wrong, and yes, she is right, 1 is not a prime number. 2 is both the first positive prime number and the only even prime number.

I remember at GCSE biology:
Teacher: "There's 33 vertebrae, so 33 spaces between them."
Me "No, if there's 33, then there's 32 spaces between them"
Teacher: "No, 33 spaces"
Me: "No look" holds up 2 fingers "one space" (repeat with 3, 4 and 5 fingers)
Teacher: "Ah. But if there's 33 then there's 33 spaces between them"
I shut up at that point with mutters of "what made 33 special?"

There are times it's easier (and safer) to just pretend to the teacher you think they're right when you know they're wrong.

Next time I see him, I must ask what's special about the number 33...

This will be why only the good teachers liked me.....

And not the primary school supply teacher who insisted you could not take 3 away from 2. I pointed out it would be a minus number, but primary school children cannot know about minus numbers (in case their brains melt) so she told the whole class that I was wrong, and there was no such thing.

I am very very good at holding a grudge!