L'an dernier ou L'annee derniere??

Question

My best friend Pierre, who until last year shared a 2-bedroom apartment with me in Paris,

The best answer is:

Mon meilleur ami Pierre, qui jusqu'à l'année dernièrer partageait un appartement de deux chambrtrois-pièces avec moi à Paris

Why can't I use l'annee derniere here?? the grammar doesn't explain!

Thanks guys... can't do accents on this page

Accepted Answer

Hi Pippa, 
I have checked the exercise and both 'l'an dernier' and 'l'année dernière' are accepted as correct so there might be glitch somewhere in the system.
Please re-post your query using the Report it button on your correction board so that we can look at it.  
Bonne Continuation!

Answer

Simple rule, which gets it right most of the time: use "an" when you refer to counting years. Use "année", when it is about the duration. When talking about a single year, you can use use either but I mostly hear "année".
In the example you quote, the emphasis is on the duration, not on counting years, therefore you would probably use "année". Here are a few sample sentences to highlight the difference:
Vous avez 30 ans? -- You are 30 years old?Ça fait des années que je ne l'ai pas vu. -- It has been years that I haven't seen him.Je l'ai vu il y a 5 ans. -- I saw him 5 years ago.Je l'ai vu l'année/ l'an dernière. -- I saw him last year.

Answer

Hi Pippa, 
As the best answer that you quote is using what you suggest I am a bit confused. Could you let us know where this sentence comes from and we'll take a look at it?

Answer

It was the french writing exercise Visiting my best friend... it was the confusion about using l'an or l'annee... chris above answered it for me. the answer given was l'an dernier but I put l'annee derniere and didn't understand why I was wrong!! Big L plates!!

Answer

Chris I am confused then as I put as my answer l'annee and it was wrong and it gave l'an dernier as the answer neither did it give any explanation why!