It might seem quite obvious, but it took me some time to find this. If you use the pluralize helper, it will always include the number, rather than just pluralizing the word:
pluralize(2, 'day') # => 2 days
Apparently, Rails monkey-patched the String class to include a pluralize function which doesn't include the number:
"day".pluralize(2) # => days
I find it quite useful if you want to style the number differently from the text in your views.