The function f is defined by

jack0997 wrote:The function f is defined by f „(x) =… √x – 20 for all positive numbers x. If p ƒ= f (q) for some positive numbers q and p, what is q in terms of p?

(A) (p +‚ 20)^2
(B) √(p + 20‚)
(C) (√p + 20)^2
(D) √(p^2 +‚ 20)
(E) (p^2 +‚ 20)^2

OA A

Pl. help me out with this question,

„f(x)… ƒ= √x – 20

=> f(q) = √q – 20

p = √q – 20

=> √q = p + 20

Squaring both sides, we have:

=> q =[spoiler] (p + 20)^2[/spoiler]

The correct answer: A

Hope this helps!

Download free ebook: Manhattan Review GMAT Quantitative Question Bank Guide

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Vienna | Kuala Lumpur | Sydney | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.

Hi jack0997,

This question can be solved by TESTing VALUES.

Based on the information in the prompt, my initial thought would be to TEST Q=400....

f(400) = 20 - 20 = 0 and that would give us P=0.

This is a problem for a couple of reasons: First, 0 is NOT positive - and we're told that P and Q have to be positive. Second, you'll notice that three of the answers (A, C and E) would all end in a 400 when you plug in P=0 (and there can't be three correct answers here). Thus, we have to look for a different 'round number' for Q, but one that's bigger than 20.

Let's TEST Q = 900

f(900) = 30 - 20 = 10, so we're looking for an answer that equals 900 when we plug in P=10. You'll find that only one answer matches...

Final Answer: A

GMAT assassins aren't born, they're made,
Rich