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If 5n/4n - x = 0.788^-1

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GRE Instructor
Joined: 10 Apr 2015
Posts: 1232
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Kudos [?]: 1113 [1] , given: 7

If 5n/4n - x = 0.788^-1 [#permalink]  14 Feb 2018, 09:54
1
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Expert's post
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Question Stats:

100% (01:58) correct 0% (00:00) wrong based on 9 sessions
If $$\frac{5n}{4n - x} = 0.788^{-1}$$, then $$\frac{x}{n} =$$

[Reveal] Spoiler:
3/50

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Brent Hanneson – Creator of greenlighttestprep.com

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Joined: 07 Jan 2018
Posts: 553
Followers: 4

Kudos [?]: 477 [1] , given: 84

Re: If 5n/4n - x = 0.788^-1 [#permalink]  15 Feb 2018, 01:13
1
KUDOS
$$0.788^-^1$$ can be expressed as $$\frac{1}{0.788}$$

we have,

$$\frac{5n}{4n - x} = \frac{1}{0.788}$$

we can equate the two numerators to get,
$$5n = 1$$ or $$n = \frac{1}{5}$$

similarly we can also equate the denominator,
$$4n - x = 0.788$$

Replace the value of n in the eqn to get,
$$4*\frac{1}{5} - x = 0.788$$
solve for x, x = $$\frac{4}{5} - \frac{788}{1000}$$ = 3/250
Now, $$X/N = \frac{3}{250} * 5 = \frac{3}{50}$$

If nothing is mentioned on input type can the ans be an equivalent decimal 0.06?
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This is my response to the question and may be incorrect. Feel free to rectify any mistakes

GRE Instructor
Joined: 10 Apr 2015
Posts: 1232
Followers: 45

Kudos [?]: 1113 [1] , given: 7

Re: If 5n/4n - x = 0.788^-1 [#permalink]  17 Feb 2018, 11:31
1
KUDOS
Expert's post
GreenlightTestPrep wrote:
If $$\frac{5n}{4n - x} = 0.788^{-1}$$, then $$\frac{x}{n} =$$

[Reveal] Spoiler:
3/50

I created this question to test a certain fraction property that the GRE likes to test: (a - b)/c = a/c - b/c
There's also (a + b)/c = a/c + b/c

Given: 5n/(4n - x) = (0.788)^(-1)
Rewrite as: 5n/(4n - x) = 1/0.788
Flip each fraction: (4n-x)/5n = 0.788
Apply above property: 4n/5n - x/5n = 0.788
Simplify: 4/5 - x/5n = 0.788
Simplify: 0.8 - x/5n = 0.788
So: x/5n = 0.012
Multiply both sides by 5 to get: x/n = 0.06
Rewrite as fraction: x/n = 6/100 = 3/50

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Brent Hanneson – Creator of greenlighttestprep.com

Re: If 5n/4n - x = 0.788^-1   [#permalink] 17 Feb 2018, 11:31
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