1class Money
 2  attr_reader :amount
 3
 4  def initialize(amount)
 5    @amount = amount
 6  end
 7
 8  def +(other)
 9    Money.new(@amount + other.amount)
10  end
11
12  def -(other)
13    Money.new(@amount - other.amount)
14  end
15
16  def ==(other)
17    @amount == other.amount
18  end
19end