Avg rating does not show in decimal.

[w3villa-amit]

When i am trying to show the avg rating in decimal like .5,1.5,2.5 then the stars formation does not happening.I change the method of product decorator like this-:
def stars
avg_rating.to_f || 0
end
But then stars does not appear i want that actual avg rating like 1.5,2.5,3.5 will also be shown in the avg rating.
Please help.