来自《耶鲁大学开放课程：金融理论 第11集 第11集》

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  So she only contributed in present value terms 25 dollars to the operation.
  所以她贡献了手术费现值的25%
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  And then the great granddaughter,
  然后是曾孙女
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  she herself looks at it as a 50 dollar contribution,
  从她自己看是贡献了五十元
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  but from the point of view of the original operation,
  但是从原手术角度来看
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  it's discounted 3 times, so by 8, so it's 12 and 1 half.
  这要折现三次 除以八得到12.5%
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  So 50 25 12 and 1 half 6 and 1 quarter, blah, blah, forever, adds up to the 100.
  所以50+25+12.5等等总计一百
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  So basically, this parable shows how a daughter
  简单说来 这个比喻说明了
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  could share the cost of her mother's operation among all the descendants,
  她的晚辈们共同承担了
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  pay completely for the operation with each generation
  母亲的手术费用
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  making the same contribution, the same sacrifice.
  每个人都做了同样的牺牲
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  Of course, the generations who make it earlier are helping the mother more,
  晚辈中付出早的给与的帮助也更多
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  but the point is, every generation has made exactly the same sacrifice and
  但关键是 每代人都做出了同样的牺牲