gmattester wrote:Is x/3 + 3/x >2
a) x<3
b) x>1
Notice that the inequality will be false if x is negative, so 1) is not sufficient. From 2), we know x is positive, so we can multiply both sides by 3x (to get rid of the fractions), and since we know x is positive, we don't need to worry about whether to reverse the inequality when we do this:
If x > 0,
x/3 + 3/x > 2
x^2 + 9 > 6x
x^2 - 6x + 9 > 0
(x-3)^2 > 0
The left side is squared so can't be negative; the inequality will be true for every value of x
except x = 3. So Statement 2) is not sufficient on its own (x could be 3), but 1) and 2) together are sufficient (x cannot be 3). C.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com
ianstewartgmat.com