如何以两位精度显示输出

Here is my code

这是我的代码

class Atm

  attr_accessor :amount, :rem, :balance

  TAX = 0.50

  def transaction

    @rem = @balance=2000.00
    @amount = gets.chomp.to_f

    if @amount%5 != 0 || @balance < @amount
      "Incorrect Withdrawal Amount(not multiple of 5) or you don't have enough balance"
    else
      @rem = @balance-(@amount+TAX)
      "Successful Transaction"
    end
  end
end

a=Atm.new
puts "Enter amount for transaction"
puts a.transaction
puts "Your balance is #{a.rem.to_f}"
class Atm

  attr_ac