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# The function f is defined by f (x) =√x − 20 for all positive numbers x

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Math Expert
Joined: 02 Sep 2009
Posts: 51100
The function f is defined by f (x) =√x − 20 for all positive numbers x  [#permalink]

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01 Oct 2018, 22:01
00:00

Difficulty:

15% (low)

Question Stats:

87% (01:00) correct 13% (02:18) wrong based on 30 sessions

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The function f is defined by f (x) =√x − 20 for all positive numbers x. If p = 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

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Math Expert
Joined: 02 Aug 2009
Posts: 7099
Re: The function f is defined by f (x) =√x − 20 for all positive numbers x  [#permalink]

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01 Oct 2018, 22:13
Bunuel wrote:
The function f is defined by f (x) =√x − 20 for all positive numbers x. If p = 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

$$f(q)=√q-20=p.............√q=p+20.......q=(p+20)^2$$...A

OR

Take p=1, so √q-20=1.....q=(20+1)^2
Look in choices
Only A matches
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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Re: The function f is defined by f (x) =√x − 20 for all positive numbers x &nbs [#permalink] 01 Oct 2018, 22:13
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# The function f is defined by f (x) =√x − 20 for all positive numbers x

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