Y5 Maths - Is really correct?

[cupofteainpeace]

Q - How many faces, vertices and edges does an octahedron have?
couldn't help ds so looked on internet for answer in hope of realising how to work it aout. Internet said..
Faces - 8 (ok)
Edges - 12(?)
Vertices - 6(?)

Am I being thick? I can't even imagine the shape?!!!

Does an octahedron have 8 triangles for its faces? There is a formula that connects faces, edges and vertices but can't remember it right now. I'm sure there will be a person better at thinking in 3d than I am along soon though

Try google images and then it makes sense.

Yes that's right, it looks like 2 pyramids with their bases joined together it that makes sense.

Looking at google images it appears to be a couple of pyramids stuck together, yes?

This looks quite useful. And has diagrams.

gwydir.demon.co.uk/jo/solid/octa.gif

This is it's net - so can work out from there nicely.

It doesn't have to have triangular faces either (but a regular one will).

Ah, didn't think of googling images!
Presumably then ds should have known what an octahedron was then!

I don't think you're thick. My DS is in year 5 and I'm convinced they're inventing new shapes to baffle me with.

Yes, DS should know. My Year 3s would know that an octahedron was a 3D shape with 8 faces (octa = 8, -hedron indicating 3D shape not 2D shape). The more able half of the class at least would be able to pick an octahedron out of a set of mixed regular 3D shapes, and the most able would identify a regular octahedron from a net.

Funnily enough, my experience is that children seem to know fewer shapes than I did as a child ... though I do think that my Year 6 teacher took it a little far when he introduced us to the stellated and truncated versions of some of the main Platonic solids!!

(Still proud, many years later, of the 'great stellated dodecahedron' I made in Year 6.....)

Will check DS's knowledge tomorrow (in year 3). He does like to wonder what an eleven sided shape would be called...I might try and find out.

Hendecagon or Undecagon in case it is the burning question for anyone else

Response from ds this morning...."Oh, yes, how could I have forgotten that?"

So, he SHOULD have known it after all.
I've learnt something too.
Thankyou all for your help. Tonights homework is a History assignment so no help from me there either! God I feel thick!

Hendecagon definitely sounds like it should be one of those overpriced build-it-yourself dragons from Warhammer.