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• ### $450 Tuition Credit & Official CAT Packs FREE February 15, 2019 February 15, 2019 10:00 PM EST 11:00 PM PST EMPOWERgmat is giving away the complete Official GMAT Exam Pack collection worth$100 with the 3 Month Pack ($299) • ### Free GMAT practice February 15, 2019 February 15, 2019 10:00 PM EST 11:00 PM PST Instead of wasting 3 months solving 5,000+ random GMAT questions, focus on just the 1,500 you need. # If x=0.2, then what is the value of x^3-1/x-1?  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics Author Message TAGS: ### Hide Tags Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 6949 GMAT 1: 760 Q51 V42 GPA: 3.82 If x=0.2, then what is the value of x^3-1/x-1? [#permalink] ### Show Tags 12 Feb 2019, 00:08 00:00 Difficulty: 25% (medium) Question Stats: 79% (01:48) correct 21% (01:21) wrong based on 28 sessions ### HideShow timer Statistics [GMAT math practice question] If $$x=0.2$$, then what is the value of $$\frac{x^3-1}{x-1}$$? $$A. 1.2$$ $$B. 1.22$$ $$C. 1.24$$ $$D. 1.44$$ $$E. 2.22$$ _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$149 for 3 month Online Course"
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If x=0.2, then what is the value of x^3-1/x-1?  [#permalink]

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12 Feb 2019, 00:12
0.2 = 2/10. $$x^3$$ = $$\frac{8}{1000}$$
$$x^3-1$$ = $$\frac{-992}{1000}$$

$$x-1 = \frac{-8}{10}$$

$$\frac{(x^3-1)}{(x-1)}$$ = $$\frac{992}{1000}*\frac{10}{8}$$ = 124/100 = 1.24

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Re: If x=0.2, then what is the value of x^3-1/x-1?  [#permalink]

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12 Feb 2019, 00:17
MathRevolution wrote:
[GMAT math practice question]

If $$x=0.2$$, then what is the value of $$\frac{x^3-1}{x-1}$$?

$$A. 1.2$$
$$B. 1.22$$
$$C. 1.24$$
$$D. 1.44$$
$$E. 2.22$$

x = 0.02

Given ,

$$\frac{x^3-1}{x-1}$$

= $$0.2^3$$- 1 / 0.2 - 1

= 0.008 - 1 / - 0.8

= - 0.992 / - 0.8

= 1.24.

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If x=0.2, then what is the value of x^3-1/x-1?  [#permalink]

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Updated on: 13 Feb 2019, 21:34

Solution

Given:
• The value of x = 0.2

To find:
• The value of the expression $$\frac{x^3 – 1}{x – 1}$$

Approach and Working:
We know that
• $$x^3 – 1 = (x – 1) (x^2 + x + 1)$$

Therefore, $$\frac{x^3 – 1}{x – 1} = x^2 + x + 1$$

Now, if x = 0.2
• The value of the given expression = $$(0.2)^2 + 0.2 + 1 = 0.04 + 0.2 + 1 = 1.24$$

Hence, the correct answer is option C.

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Originally posted by EgmatQuantExpert on 12 Feb 2019, 01:36.
Last edited by EgmatQuantExpert on 13 Feb 2019, 21:34, edited 1 time in total.
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Re: If x=0.2, then what is the value of x^3-1/x-1?  [#permalink]

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12 Feb 2019, 20:09
MathRevolution wrote:
[GMAT math practice question]

If $$x=0.2$$, then what is the value of $$\frac{x^3-1}{x-1}$$?

$$A. 1.2$$
$$B. 1.22$$
$$C. 1.24$$
$$D. 1.44$$
$$E. 2.22$$

((0.2)^3 - 1)/(0.2 - 1)

(0.008 - 1)/(-0.8)

(-0.992)/(-0.8) = 1.24

Alternate solution:

The formula for factoring the difference of cubes is (x^3 - 1) = (x - 1)(x^2 + x +1). We can use that fact to simplify (x^3 - 1)/(x - 1) = x^2 + x + 1. Therefore, when x = 0.2, we have:

(0.2)^2 + 0.2 + 1 = 0.04 + 0.2 + 1 = 1.24

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Re: If x=0.2, then what is the value of x^3-1/x-1?  [#permalink]

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14 Feb 2019, 01:02
=>

$$\frac{x^3-1}{x-1} = \frac{(x-1)(x^2+x+1)}{x-1}= x^2+x+1$$

Plugging in $$x = 0.2$$ yields
$$x^2+x+1 = (0.2)^2 + (0.2) + 1 = 0.04 + 0.2 + 1 = 1.24$$

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Re: If x=0.2, then what is the value of x^3-1/x-1?   [#permalink] 14 Feb 2019, 01:02
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