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

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GRE Instructor
Joined: 10 Apr 2015
Posts: 1530
Followers: 55

Kudos [?]: 1458 [1] , given: 8

If 5n/4n - x = 0.788^-1 [#permalink]  14 Feb 2018, 09:54
1
KUDOS
Expert's post
00:00

Question Stats:

85% (01:55) correct 14% (00:48) wrong based on 14 sessions
If $$\frac{5n}{4n - x} = 0.788^{-1}$$, then $$\frac{x}{n} =$$

[Reveal] Spoiler:
3/50

_________________

Brent Hanneson – Creator of greenlighttestprep.com

Director
Joined: 07 Jan 2018
Posts: 598
Followers: 7

Kudos [?]: 538 [1] , given: 88

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?
_________________

This is my response to the question and may be incorrect. Feel free to rectify any mistakes

GRE Instructor
Joined: 10 Apr 2015
Posts: 1530
Followers: 55

Kudos [?]: 1458 [1] , given: 8

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

RELATED VIDEO

_________________

Brent Hanneson – Creator of greenlighttestprep.com

GRE Instructor
Joined: 10 Apr 2015
Posts: 1530
Followers: 55

Kudos [?]: 1458 [1] , given: 8

Re: If 5n/4n - x = 0.788^-1 [#permalink]  21 Jan 2019, 06:13
1
KUDOS
Expert's post
amorphous wrote:
If nothing is mentioned on input type can the ans be an equivalent decimal 0.06?

Great question!

On the GRE, you will be told when to enter your response as a fraction. You will be given two boxes (one box for the numerator and one box for the denominator) to enter values. If there's just one box, then you can enter the value as a decimal.

When I first posted the question, I forgot to add directions to submit the answer as a fraction. I have now added text to that effect.

For more on how to enter values in Numeric Entry questions, watch 2:00 to 5:10 of the following video: https://www.greenlighttestprep.com/modu ... video/1244

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com

Re: If 5n/4n - x = 0.788^-1   [#permalink] 21 Jan 2019, 06:13
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