karna2129 wrote:
PrashantPonde wrote:
Question: If 3x + 5 < x + 11, is x prime?
Simplify equation to x<3. Hence question becomes is x=2?
(1) the sum of x and y is even
INSUFFICIENT: We dont know y
(2) The product of x and y is odd.
INSUFFICIENT: We dont know whether y is integer
e.g. x=2, y=1.5 then xy=3 (ODD)
e.g. x=1, y=3 then xy=3 (ODD)
x can be 1 or 2, hence its not sufficient.
Combining (1) & (2)
SUFFICIENT:
If x = 2, y must be 1.5 or -1.5 to make xy (ODD), however x + y cannot be EVEN.
If x = 2, y must be 0 or even to make x + y (EVEN), however xy cannot be ODD
Thus if x=2, both statements cannot be true simultaneously.
This information is SUFFICIENT to prove x cannot be 2.
Hence choice(C) is the answer.
According to my knowledge 1 is Neither Prime nor Composite.
Please correct me if GMAT thinks the other way.
I am really concerned about this
GMAT doe not have some kind of their own math.
Facts about primes:
1. 1 is not a prime, since it only has one divisor, namely 1.
2. Only positive numbers can be primes.
3. There are infinitely many prime numbers.
4. the only even prime number is 2. Also 2 is the smallest prime.
5. All prime numbers except 2 and 5 end in 1, 3, 7 or 9.
Theory on Number Properties:
math-number-theory-88376.htmlNumber Properties - Tips and hints:
tips-and-hints-for-specific-quant-topics-with-examples-172096.html#p1371030All DS Number Properties Problems to practice:
search.php?search_id=tag&tag_id=38All PS Number Properties Problems to practice:
search.php?search_id=tag&tag_id=59