Critical Reasoning

If A, then B.
If B, then C.
If C, then D.

If all of the statements above are true, which of the following must also be true?

(A) If D, then A.

(B) If not B, then not C.

(C) If not D, then not A.

(D) If D, then E.

(E) If not A, then not D

OA later

IMO A

sarthak wrote:OA is C

Can you please explain.

IMO it is B This is a 'must be true' question. hence, the answer must be from the information contained in the original statement.

Very confusing. Can you pls give the original explanation.

I am very doubtful whether this is a GMAT type question.

This is actually a LSAT problem . Which is supposed to be 1 step tougher than GMAT in CR. So its good to practice couple of problems from there to keep prepared.


And alas ... I only have the OA ... no explanation.IMO B and E

sarthak wrote:If A, then B.
If B, then C.
If C, then D.

If all of the statements above are true, which of the following must also be true?

(A) If D, then A.

(B) If not B, then not C.

(C) If not D, then not A.

(D) If D, then E.

(E) If not A, then not D

OA later

if A implies B, then negation B implies negation A. So C

I think it is C because from the sequence it shows that A through the process will always lead to D.

Hence If D does not exist then A was never there. Because if A were there then it would lead to B, then C and then D. But if there is no D then there was no A.

I know it is real confusing but hope I made sense.

mj41 wrote:I think it is C because from the sequence it shows that A through the process will always lead to D.

Hence If D does not exist then A was never there. Because if A were there then it would lead to B, then C and then D. But if there is no D then there was no A.

I know it is real confusing but hope I made sense.

Can't the same argument be made of E? Why not E?

Make sure you know the difference between a sufficient condition

If A, then B (For B to be true, it is sufficient that A is true)

and a necessary condition

If not A, then not B. (B is true only if A is true. This is not to say that B is true if A is true) For B to be true, A must be true. That A is true does not necessarily mean that B is true


Note that if A implies B (A is sufficient condition for B), not B implies not A (B is a necessary condition for A)


Think of the following

A- is a GMAT student
B- speaks at least some English
C- is a human being
D- is a mammal
E- loves Dorothy Parker's short stories

Tried depicting the logic in a diagram invloving concentric circles
where A is the innermost circle and D the outer most.
If A then B so A is a subset of B so the circle A is completely inside B
if B then C so B is subset of C so A is inside B which inturn is inside C
if C then D so C is a subset of D.
Tried labelling them as Kevin has done in his post. With A as those who are taking GMAT and D as Mammals.
Finding the correct answer C is easier.