Ruby on Rails: the percentage of the total does not work

I have to calculate how many% of survivors (end points) were removed and how many were not, but I do not know how to do it, but it did not work, I do not know if I did not say it on the routes … I used this method here in the model

def percentage_abducted
if (removed == true)
back removed / servivor.all * 100
d & # 39; other
back removed / servivor.all * 100
end
end