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If f(a, b) = a2b4, and f(m, n) = 5, what is the value of f(3

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GRE Prep Club Legend
Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 105

Kudos [?]: 1783 [0], given: 397

If f(a, b) = a2b4, and f(m, n) = 5, what is the value of f(3 [#permalink]  30 Jul 2018, 09:49
Expert's post
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Question Stats:

50% (00:17) correct 50% (04:16) wrong based on 4 sessions
If $$f(a, b) = a^2b^4$$, and $$f(m, n) = 5$$, what is the value of f(3m, 2n)?

[Reveal] Spoiler: OA
720

_________________

Sandy
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GRE Prep Club Legend
Joined: 07 Jun 2014
Posts: 4857
GRE 1: Q167 V156
WE: Business Development (Energy and Utilities)
Followers: 105

Kudos [?]: 1783 [0], given: 397

Re: If f(a, b) = a2b4, and f(m, n) = 5, what is the value of f(3 [#permalink]  31 Jul 2018, 14:20
Expert's post
Explanation

Plug m and n into the function in place of a and b. If f(m, n) = 5, then:
$$m^2n^4 = 5$$

This cannot be further simplified, so continue to the second part of the problem: plug $$3m$$ and $$2n$$ into the function for a and b:

$$f(3m, 2n) = (3m)^2(2n)^4 = 9m^2 16n^4 = 144m^2n^4$$

Since $$m^2n^4 = 5$$, $$144m^2n^4 = 144(5) = 720$$.
_________________

Sandy
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Re: If f(a, b) = a2b4, and f(m, n) = 5, what is the value of f(3   [#permalink] 31 Jul 2018, 14:20
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