How can we assume there is any incorrectly addressed mail at all?

@Garry, Happy to help, and we're thrilled you're loving the course so far! Keep up the great work! :) From the stimulus, we know that we have two types of mail. 1) correctly addressed mail 2) incorrectly addressed mail We know that correctly addressed mail always arrives on time unless it's damaged. For incorrectly addressed mail, we don't know anything. We're also told that most mail arrives late. That's odd. This means that most mail either is incorrectly addressed or it's correctly addressed and damaged. However, we also know from the stimulus that at most only a few of the correctly addressed mail is late. We know this because we're told in the first sentence that "Nearly all mail that is correctly addressed arrives at its destination within two business days of being sent." This means that it must be the case that there is a lot of mail that's incorrectly addressed. The question asks, "If the statements above are true, which one of the following must be true?" You asked how we can rule out the possibility that all mail is correctly addressed. The reason that we can rule out this possibility is because if all mail were correctly addressed, then there is no way that most mail could arrive three business days or more after being sent. We know this because of the first premise, which tells us that nearly all (most) mail that's correctly addressed arrives at its destination within two business days. If the scenario you're proposing were true, then we would be directly contradicting the first premise of the stimulus, so we know this can't be true. The ONLY way for a majority of all mail to arrive 3 business days or more is if a huge proportion of it is incorrectly addressed. We know this because a majority of correctly addressed mail arrives within two business days, so the late mail has to come from somewhere (and it's coming from incorrectly addressed mail). (D) says, "A large proportion of mail is incorrectly addressed." (D) has to be true because we know that most mail arrives late, and we also know that most correctly addressed mail arrives at its destination on time. This means that in order for most of ALL mail to be late, a very large fraction of all mail has to be incorrectly addressed. Does this make sense? Let us know if you have any more questions—we're here to help!