Help me help Dniece with homework!!!

[Fandangulous]

The subject is contract law:

John places an ad in a magazine: 'model trains for sale £200. First offer of £200 will secure the lot.'

Is this an offer or an invitation to treat?

I believe that most adverts are intention to treat, as they state the terms of a contract without actually entering into a contract for an item or a service.

Invitation to treat.
What kind of homework is she doing??

Oh gosh thank you so much! She's doing a level law and is getting on brilliantly but wanted to double check that particular question with me as, I'm throughly ashamed to say, I have a law degree it is ancient though and I've never used it.

I knew all ads were invitations to treat but remembered there can be exceptions and then worried because it had the words 'first offer'... then I completely panicked, made my excuses to get off the phone and ran to MN