Solve float point error

sum.rb

def sum(a, b)
  a_dec = a.to_s.split('.')[1]
  b_dec = b.to_s.split('.')[1]

  len1 = a_dec ? a_dec.size : 0
  len2 = b_dec ? b_dec.size : 0
  max_len = len1 > len2 ? len1 : len2
  factor = 10 ** max_len

  if max_len > 0
    (a * factor + b * factor) / factor.to_f
  else
    a + b
  end
end

p 0.1 + 0.2
p 1.1 - 1
p 1 + 2
p "---------------"
p sum(0.1, 0.2)
p sum(1.1, -1)
p sum(1, 2)