Vieux - singular or/and plural?

Question

Hi,I thought that "vieux" can be singular AND  plural but the quiz says it is only singular.

Cécile Janty-Davies · Accepted Answer

Hi Larry, 
The adjective 'vieux' can be singular or plural as in -
un vieux manteau = an old coat 
un vieux copain = an old friend
but in front  an -h mute or a vowel, it will become 'vieil' -  
un vieil homme 
un vieil hotel 
un vieil ami 
In the plural -
C'était de vieux amis = They were old friends
C'était de vieux hotels = They were old hotels
etc.

Chris Wirt · Answer

In the lesson it says that vieux doesn't change in the masculine plural -- and it doesn't (as opposed to beu, for example):Le vieux homme -- The old man.Les vieux hommes -- The old men.But there is a different form of vieux for the masculine singular, if the noun starts with a vowel or h muet:Un vieil amour. -- An old love.