thevenus wrote:

Bunuel, please throw some light here,

(c) is right as per many of us but why not (E)?

Is x divisible by 15?(1) When

x is divided by 10, the result is an integer -->

\frac{x}{10}=integer -->

x=10*integer. Now, if

x=0 (in case

integer=0), then the answer is YES but if

x=10 (in case

integer=1), then the answer is NO. Not sufficient.

From this statement though we can deduce that

x is an integer (since

x=10*integer=integer).

(2)

x^2 is a multiple of 30 --> if

x=0, then the answer is YES but if

x=\sqrt{30}, then the answer is NO. Not sufficient.

(1)+(2) Since from (1)

x=integer then

x^2=integer, and in order

x^2 to be divisible by 30=2*3*5,

x must be divisible by 30 (

x must be a multiple of 2, 3 and 5, else how can this primes appear in

x^2?), hence

x is divisible by 15 too. Sufficient.

Notice that x can be positive, negative or even zero, but in any case it'll be divisible by 30.Answer: C.

Next,

every GMAT divisibility question will tell you in advance that any unknowns represent positive integers (ALL GMAT divisibility questions are limited to positive integers only). So, we edited this question and in the new

GMAT Club tests this question reads:

If x is a positive integer, is x divisible by 15?(1) x is a multiple of 10 --> if

x=10, then the answer is NO but if

x=30, then the answer is YES. Not sufficient

(2) x^2 is a multiple of 12 --> since

x is an integer, then

x^2 is a perfect square. The least perfect square which is a multiple of 12 is 36. Hence, the least value of

x is 6 and in this case the answer is NO, but if for example

x=12*15 then the answer is YES. Not sufficient.

Notice that from this statement we can deduce that

x must be a multiple of 3 (else how can this prime appear in

x^2?).

(1)+(2)

x is a multiple of both 10 and 3, hence it's a multiple of 30, so

x must be divisible by 15. Sufficient.

Answer: C.

Hope it's clear.

Wasn't the previous one was tougher? why did you changed / modified ? Now the GMAT can't put such an option (of choosing irrational no. at least if not negative numbers?)