BN1989
If w > x > y > z > 0, is z < 4?
(1) \(\frac{1}{w} +\frac{1}{x} +\frac{1}{y} +\frac{1}{z}\)\( = 1\).
(2) \(\frac{1}{w} > \frac{1}{4}\).
from gmatquantproblems
We are dealing with positive numbers and z is the smallest of the four.
Stat (1)We cannot solve this equation, but we can see that if z is too large then the left side will be less than 1. There must be a smallest number that will work. As a boundary case, we could use z = 4. Let's even say that all four variables equal 4. In that case,
> \(\frac{1}{w} +\frac{1}{x} +\frac{1}{y} +\frac{1}{z} = \frac{1}{4} +\frac{1}{4} +\frac{1}{4} +\frac{1}{4}\)\( = 1\)
But even if z = 4, the other fraction will have to be slightly less than \(\frac{1}{4}\), so it could not equal 1. That's if z = 4. If z is larger than 4, then it couldn't possibly equal 1.
Thus, z must be less than 4.
SufficientStat (2)You can multiply both sides by w and 4 to get rid of the fractions.
> \(\frac{1}{w} > \frac{1}{4}\)
> \(4 > w\)
If w < 4, then we can use the fact that z < w to conclude that z < 4.
Sufficient(d) EACH statement ALONE is sufficient to answer the question asked.