Ruby String formating

def labor_hours
ar = []
(0..39).each do |n|
a = n.to_f
b = a + 0.25
c = a + 0.50
d = a + 0.75
ar.push([sprintf('%0.2f', a), a],[sprintf('%0.2f', b), b],[sprintf('%0.2f', c), c],[sprintf('%0.2f', d), d])
end
ar.push(["40.00",40])
end