一个人有50元，买了袜子20元，剩30元，然后买了水果15元，剩15元，接着买了饼干9元，剩下6元，最后坐车6元，请问为什么所有剩下的钱加起来是51元？

为什么呢？因为把每次剩下的钱加起来，本来就是51元啊！为什么一定要是50元呢？

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