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# If f(2a) = 2f(a) and f(6) = 11, what is the value of f(24)?

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GMAT Club Legend
Joined: 07 Jun 2014
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If f(2a) = 2f(a) and f(6) = 11, what is the value of f(24)? [#permalink]  30 Jul 2018, 09:45
Expert's post
00:00

Question Stats:

92% (01:06) correct 7% (01:14) wrong based on 13 sessions
If $$f(2a) = 2f(a)$$ and $$f(6) = 11$$, what is the value of f(24)?

(A) 22
(B) 24
(C) 44
(D) 66
(E) 88
[Reveal] Spoiler: OA

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Sandy
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Intern
Joined: 10 Aug 2018
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Re: If f(2a) = 2f(a) and f(6) = 11, what is the value of f(24)? [#permalink]  11 Aug 2018, 13:30
Here you need to note the given formulae and try to use them.

24 = 2*2*6

So f(24) = f(2(2*6)) = 2f(2*6) = 2*2f(6) = 4*f(6) = 4*11 = 44

So C.
GMAT Club Legend
Joined: 07 Jun 2014
Posts: 4749
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 93

Kudos [?]: 1659 [0], given: 396

Re: If f(2a) = 2f(a) and f(6) = 11, what is the value of f(24)? [#permalink]  12 Aug 2018, 07:16
Expert's post
Explanation

This question concerns some function for which the full formula is not provided. The problem indicates that f(2a) = 2f(a). In other words, this function is such that plugging in 2a is the same as plugging in a and then multiplying by 2. Plug f(6) = 11 into the equation f(2a) = 2f(a):

$$f(2(6)) = 2(11)$$

$$f(12) = 22$$

Use the same process a second time. If a = 12 and f(12) = 22:

$$f(2(12)) = 2(22)$$

$$f(24) = 44$$
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Sandy
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Re: If f(2a) = 2f(a) and f(6) = 11, what is the value of f(24)?   [#permalink] 12 Aug 2018, 07:16
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