Critical Reasoning

Comcorp Shipping Clerk: Last week, no shipments of building supplies were sent out on friday. The five specially ordered shipments sent out last week were sent out on Thursday, and each of those specially ordered shipments consisted entirely of building supplies. Four shipments were sent to Truax Construction last week, none of which consisted of building supplies.

If the shipping clerk's statements are true, which of the following must also be true?

a. All of Comcorp's shipments of building supplies last week were specially ordered.
b. None of Comcorp's shipments sent on friday of last week was sent to Truax Construction.
c. None of the shipments sent by Comcorp by Truax Construction last week was specially ordered.
d. None of Comcorp's shipments sent on thursday of last week was sent to Truax Construction.
e. All of Comcorp's shipments of building supplies last week were sent out on thursday.

What is the best way to solve this problem please ?

IMO C

Look at the facts presented and then apply them to the answer choices.

Fact 1: No shipments of building supplies were sent out on Friday.
Fact 2: The five specially ordered shipments sent out last week were sent out on Thursday
Fact 3: All five of those shipments consisted entirely of building supplies.
Fact 4: Four shipments were sent to Truax Construction last week
Fact 5: None of the shipments to Truax consisted of building supplies

If the shipping clerk's statements are true, which of the following must also be true?

a. All of Comcorp's shipments of building supplies last week were specially ordered. Incorrect. We know that five shipments of building supplies were specially ordered. There is no mention that these were the only special orders of building supplies.

b. None of Comcorp's shipments sent on friday of last week was sent to Truax Construction. Incorrect. No shipments of building supplies were sent out on Friday. Truax did not order building supplies so it is possible that their shipments were sent on Friday.

c. None of the shipments sent by Comcorp by Truax Construction last week was specially ordered. Correct. The fact set states, "The five specially ordered shipments sent out last week were sent out on Thursday" I interpret the choice of the word "the" in the statement to mean that the five specially ordered shipments were the only ones sent last week.

d. None of Comcorp's shipments sent on thursday of last week was sent to Truax Construction. Incorrect. Five specially ordered shipments were sent on Thursday. These five shipments were of building supplies so we know they did not go to Truax. However, it is not stated that these were the only shipments sent on Thursday. It is possible Truax's shipments also went out on Thursday.

e. All of Comcorp's shipments of building supplies last week were sent out on thursday. Incorrect. Five shipments of building supplies were sent out on thursday. It is not stated that these were the only five. Additional shipments of building supplies may have been sent earlier in the week.

I would add to this but rkanthilal did a perfectly good job of addressing the answers. Good work!

Jared

Let me jump in here and build on the excellent explanation given by rkanthilal.

What you asked for is the "best way to solve the problem." So let's generalize a little bit to apply to other questions...

Well, for an inference question such as this one, the correct answer must be true. For GMAT inference questions the best technique is not to try and find the correct answer, but rather to look for 4 answer choices that could be false. Process of elimination is the key. It is easier to find the four answers that are wrong (because they could be wrong) So you see? You don't have to show that they are false - only that they could be.

There are 4 great ways for an answer choice to meet the could be false criteria:

1) Beyond the scope of the stimulus

2) A Prediction (often these appear as if...then...statements)

3) Must be False

4) Choices that tell people what to do ("You should study hard" is not actually must be true.)


With a question like this one that seems to be more detail-oriented than most inference, I would ask myself "Do we know that ..." so for choice A "Do we know that ALL of the shipments were specially ordered?" No.

These answer choices are:

A. Beyond the scope. Don't know that ALL are specially ordered.
B. Beyond the scope. Don't know what day the shipments to Truax were made.
C. Leave it since it appears to be on topic.
D. Beyond the scope. We don't know that NO shipments were sent to Truax on Thursday.
E. Beyond the scope. We don't know that ALL of the shipments were sent on Thursday.

Jared and David...Thanks for your nice comments...

Thanks David, it is very helpful!!