Input number multiplies as a string instead of number - Rails 4

I want you to focus on the line conversion = value * 7.50061

Consider the following. When i print the conversion with an initial value of 12, i get seven times 12 like this 12121212121212 . Propably thats because i am multiplying a string but when i tried

value.to_i i had an error saying implicit conversion from float to string??

i submit a value from an input element in the view and i input it from the CalculationsController to the CalculationsHelper

module CalculationsHelper

  # parameter1 = Sa02, parameter2 = Hgb, parameter3  = PaO2
  def AOC(parameter1,parameter2,parameter3,unit_parameter2,unit_parameter3)
    # CaO2 = ( Hgb * 1.34 * SaO2 / 100 ) + ( PaO2 * 0.031 )
    if (unit_parameter3 != "mmHg")
      puts "entered conversions"
      conversions(unit_parameter3,parameter3, "mmHg")
    end
  end

  def conversions(input, value, target)
    if (target == "mmHg")
      if (input == "Kpa")
        puts "this is the value before " + value
        conversion = value * 7.50061
        puts "this is the " + conversion
      end
    end
  end

end

CalculationsController

class CalculationsController < ApplicationController
  include CalculationsHelper

  def index

  end

  def calculation

    if (params["equation"] == "AOC")
      puts "entered AOC"
      AOC(params["parameter1"],params["parameter2"],params["parameter3"],params["unit_parameter2"],params["unit_parameter3"])
    end
    respond_to do |format|
      format.json {
        render json: { success: "ok" }
      }
    end
  end
end

any help appreciated