Hi, Hussein and Gustavo,
I completely agree with Gustavo's answer and I see that all his examples are very natural, but I'd like to refer to the fact that in our curriculum, we have the following sentence:
- The tour guide said that ten is the least number of tourists she can take on the boat trip.
- First, I found it strange to use 'less / least' before 'number', but two of my friends have told me that it is possible to use 'number' to mean 'quantity' and that the sentence is correct as it is. (All the outside books have included 'less number' in their books now).
- On LDOCE (fifth definition), the word 'number' is listed as an uncountable noun meaning an amount of something that can be counted. So, controversially, I think that it is possible to use Hussein's first sentence even if it isn't idiomatic.