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What is 20% of 3x?

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What is 20% of 3x?

by Gmat_mission » Sun Jun 24, 2018 11:40 pm

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What is 20% of 3x?

(1) 40% of 6x equals 12

(2) 20x = 15x + 25

[spoiler]OA=D[/spoiler].

I don't know how to answer the question. How can I use each statement? Please, someone give me some help.
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by Vincen » Mon Jun 25, 2018 1:14 am

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Hello Gmat_mission.

Here, we have to find the value of 20% of 3x, that is to say, 0.2*3x.

First Statement
(1) 40% of 6x equals 12
This statement tells us that $$12=40\%\cdot6x\ \ \Rightarrow\ \ 12=2\cdot0.4\cdot3x\ \ \Rightarrow\ \ 12=2\cdot2\cdot\left(0.2\cdot3x\right)\ \Rightarrow\ \ \ 0.2\cdot3x=3.$$ So, this statement is sufficient.

Second Statement
(2) 20x = 15x + 25
From this statement we get $$20x=15x+25\ \Rightarrow\ \ 5x=25\ \Rightarrow\ \ x=5\ \ \ \Rightarrow\ \ 3x=15\ \ \Rightarrow\ \ 0.2\cdot3x=0.2\cdot 15\ \Rightarrow\ \ 0.2\cdot3x=\frac{1}{5}\cdot 15=3.$$ So, this statement is sufficient.

Therefore, the answer is the option D.

I hope it helps you.
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by [email protected] » Tue Jun 26, 2018 9:41 am

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Hi Gmat_mission,

We're asked for the value of 20% of 3X. This question involves a great Algebra 'shortcut' that you can use to avoid doing lots of math. To answer this question, we need to know the value of X.

1) 40% of 6X equals 12

The information in Fact 1 allows us to create 1 equation with 1 variable:
(.4)(6X) = 12

At this point, you COULD solve for X (and there would be just one answer), so you WOULD know the value of X and there would be just one answer to the question. You don't actually have to do the math to know that.
Fact 1 is SUFFICIENT

2) 20X = 15X + 25

Just as in Fact 1, the information in Fact 2 gives us 1 equation with 1 variable. At this point, you COULD solve for X (and there would be just one answer), so you WOULD know the value of X and there would be just one answer to the question. You don't actually have to do the math to know that.
Fact 2 is SUFFICIENT

Final Answer: D

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Rich
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