In the telephone number 936-215X

[Nicky]

In the telephone number 936-215X, what digit does X represent?


(1) Only one digit in the telephone number is greater than X.
(2) X is the greatest of the digits not among the telephone number’s first six digits.

Source: My GMAT Prep School

[Guest]

In the telephone number 936-215X, what digit does X represent?


(1) Only one digit in the telephone number is greater than X.
(2) X is the greatest of the digits not among the telephone number’s first six digits.

Source: My GMAT Prep School

is answer is D ?

[Phins2713]

I believe the answer is B.

Statement 1 is not sufficient because X could be 7 or 8 and this statement would be true. Only one digit (9) in the telephone number is greater than 7 or 8.

Statement 2 is sufficient because 8 is the greatest of the digits not among the telephone number's first six digits. This statement is sufficient without referencing the first statement.

[RonPurewal]

I believe the answer is B.

Statement 1 is not sufficient because X could be 7 or 8 and this statement would be true. Only one digit (9) in the telephone number is greater than 7 or 8.

Statement 2 is sufficient because 8 is the greatest of the digits not among the telephone number's first six digits. This statement is sufficient without referencing the first statement.

correct, but, one caveat.

in statement 1, x could also be 6. in this case, there will still be only one digit that's greater than x. there's now one digit that equals x, but ... we don't care.

fortunately for you, this doesn't matter on this particular problem, because you've already proved that the statement is insufficient (7 or 8 --> two different possibilities --> insufficient).
HOWEVER,
if the phone number were 937-215x, then statement 1 would still be insufficient, because x could still be either 7 or 8. using your line of reasoning above, you would mistakenly conclude that x could only be 8, and you would erroneously classify the statement as sufficient.

remember, "not greater than" doesn't mean "less than"; it means "less than or equal to". this is a crucial distinction; learn it.

other than that, well played.