CR # 3

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 175
Joined: Mon Feb 09, 2009 3:57 pm
Thanked: 4 times

CR # 3

by tom4lax » Sun Sep 06, 2009 12:49 pm
OA is D

Would be interested to hear people's reasoning as I chose C
Attachments
CR 3.jpg

Junior | Next Rank: 30 Posts
Posts: 23
Joined: Mon Apr 27, 2009 7:59 am
Location: London
GMAT Score:640

by BrianSmith » Sun Sep 06, 2009 11:00 pm
IMO it's D.

If most mail arrives within 3+ days, and most correctly addressed mail arrives within 2 days, then most mail is cannot be correctly addressed. This means, D - a large proportion of mail is incorrectly addressed.

B tries to claim that a lot of the correctly addressed mail is damaged. However, this is not possible as we know most correctly addressed mail arrives in 2 days, which means it is not damaged.

As for C, it plays on the first line in the argument, but reverses it. Notice that the fact most A is B does not automatically mean most B is A. So the fact most correctly addressed mail arrive within 2 days, doesn't mean most mail arriving within 2 days is correctly addressed. There could be a large amount of 'lucky' incorrectly-addressed mail which also arrives within two days. This does not contradict the fact most (but not all) mail takes longer than 3 days - for example:

10% correctly-addressed mail arriving within 2 days
14% 'lucky' incorrectly-addressed mail arriving within 2 days
1% damaged correctly-addressed mail arriving within 2+ days
75% incorrectly-addressed mail arriving withing 3+ days

In this example, most mail arriving in 2 days is incorrectly-addressed, eliminating C.

Master | Next Rank: 500 Posts
Posts: 175
Joined: Mon Feb 09, 2009 3:57 pm
Thanked: 4 times

by tom4lax » Mon Sep 07, 2009 12:27 pm
Ahhh, ok. Good explanation, thanks.