Is positive integer z greater than 275?

Is positive integer z greater than 275?

(1) z is a multiple of 21
z is multiple of 21 => z can be = 21,42.....
Clearly Insufficient

(2) z is a multiple of 39
z is multiple of 39 => z can be = 39,78.....
Clearly Insufficient

1+2
Z is multiple of 21 and 39 => minimum value of z = LCM of 21 and 39 = 3*7*13 = 273
So here we have atleast 1 value of z less than 275
Insufficient

Answer:E

The answer is E
Statement 1
The value of the multiple can be greater than 275 of lesser than 275 hence insufficient
Statement 2
Again the value can greater or lesser than 275 not sufficient
Taking both the statements together
We have LCM of 21 and 39 =273
Thus it can also be greater than or lesser than 275
So insufficient

Target question: Is positive integer z greater than 275?

Statement 1: z is a multiple of 21
Let's TEST some values.
There are several values of z that satisfy statement 1. Here are two:
Case a: z = 21, in which case, the answer to the target question is NO, z is NOT greater than 275
Case b: z = 2100, in which case, the answer to the target question is YES, z IS greater than 275
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: z is a multiple of 39
Let's TEST values again.
Case a: z = 39, in which case, the answer to the target question is NO, z is NOT greater than 275
Case b: z = 3900, in which case, the answer to the target question is YES, z IS greater than 275
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 1 tells us that z is a multiple of 21, which means we can write z = 21k for some integer k
Statement 2 tells us that z is a multiple of 39, which means we can write z = 39j for some integer j
Saying that z = 21k is the same as saying that z = (3)(7)(k)
Saying that z = 39j is the same as saying that z = (3)(13)(j)
When we write z is these two ways, we can see that (3)(7)(13) will be a multiple of 21 AND a multiple of 39
(3)(7)(13) = 273, so z COULD equal 273, in which case, the answer to the target question is NO, z is NOT greater than 275
Or it could be the case that z = (3)(7)(13)(2) = 546, in which case, the answer to the target question is YES, z IS greater than 275
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,
Brent

GMATPrepNow Or it could be the case that z = (3)(7)(13)(2) = 546, in which case, the answer to the target question is YES, z IS greater than 275

I didn't get this part, how 2 came ?

When we combine the statements, we know that z must be divisible by 3, 7 and 13
In other words, z must be divisible by 273
In other words, z is a multiple of 273

So, it COULD be the case that z = 273
Or it could be the case that z = (2)(273)
Or it could be the case that z = (3)(273)
Or it could be the case that z = (4)(273)
...or any other multiple of 273.

Does that help?

Cheers,
Brent

Yes it does, thank you

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