Do you use always a hyphen in between written numbers?

For example, would it be -

A twenty three year old oak tree, or, a twenty-three year old oak tree.

Are numbers always hyphenated, no matter what subject they are used for?

Am I right in thinking that once you get to a hundred you write it in numbered form as in -

A 200 year old oak tree, or would it be, a two hundred year old oak tree?

Grrr I should know this but my mind's frazzled!

Kat

yes, you hyphenate nos 21-99.

As far as I know, the rest is just house-style/personal preference. Newspapers have whole rule books about this!

Some places say you use figures after ten. Some places say use figures after ten EXCEPT if you begin a sentence. So;

Today 29 oak trees were cut down in the park.

But

Twenty-nine oak trees were cut down in the park today.

However I think this is just down to the particular preference of the journal/publisher/whatever.

I thought standard practice was to use figures from 10 onwards? I think that hyphenation goes further, though, e.g. a 10-year-old boy.

Yes, you hyphenate when you use numbers as adjectives - but that's slightly different. It also applies to some other kinds of compound adjectives.

So you would say:

"She jumped from the tenth floor."

but

"She jumped from a tenth-floor window."

As far as I know, there's no concrete answer about when to switch to figures, different places have different house styles. For example some places say if you have a number under ten and a number over ten in a sentence, it's better to be consistent. So you wouldn't write;

"The summer she turned ten was long and golden; the summer she turned 11 was entirely different."

You would write, "the summer she turned eleven" to maintain consistency with the ten.

Thanks for the replies, that all makes sense

Kat x