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Math Expert V
Joined: 02 Sep 2009
Posts: 59629
What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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3
16 00:00

Difficulty:   15% (low)

Question Stats: 81% (01:49) correct 19% (02:15) wrong based on 907 sessions

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What is the value of $$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$ ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

Problem Solving
Question: 121
Category: Algebra Simplifying algebraic expressions
Page: 77
Difficulty: 600

The Official Guide For GMAT® Quantitative Review, 2ND Edition

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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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20
2

$$2x^2 - 12.4x - 1.7$$

$$2x(x - 1.2) - 1.7$$

Placing the value x = 0.7

2 . 0.7 (-0.5) - 1.7

-0.7 - 1.7

= -2.4

Originally posted by PareshGmat on 03 Mar 2014, 02:33.
Last edited by PareshGmat on 14 Jul 2014, 21:23, edited 2 times in total.
##### General Discussion
Math Expert V
Joined: 02 Sep 2009
Posts: 59629
Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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1
SOLUTION

What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

$$2x^2 - 2.4x - 1.7 =$$

$$= 2*0.7^2 - 2.4*0.7 - 1.7 =$$

$$= 2*0.49 - 1.68 - 1.7 =$$

$$= -2.4$$.

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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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2
1
[2(7)(7)-24(7)-170]/100
=-2.4
D
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GMAT 1: 590 Q45 V27 Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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1
2(0.7)^2 - 2.4(0.7) - 1.7
= 2(0.49) - 1.68 - 1.7
= 0.98 - 1.68 - 1.7
= -2.4

Ans is (D)
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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1
2*49*10^(-2) - 24*7*10^(-2) - 170*10^(-2) = -240*10^(-2) = -2,4

Update
$$x(2x-2,4)-1,7 = 0,7(1,4-2,4)-1,7 = -0,7-1,7=-2,4$$
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

Problem Solving
Question: 121
Category: Algebra Simplifying algebraic expressions
Page: 77
Difficulty: 600

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$$2x^2$$ - $$2.4x$$ - 1.7 ; given x = 0.7

Or, $$2(0.7)^2$$ - $$2.4(0.7)$$ - $$1.7$$

Or, $$2(0.49)$$ - $$2.4(0.7)$$ - $$1.7$$

Or, $$0.98$$ - $$1.68$$ - $$1.7$$

Or, $$- 2.40$$

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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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[quote="Bunuel"]The Official Guide For GMAT® Quantitative Review, 2ND Edition

What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

2*0.7*0.7-2.4*0.7-1.7
.98-1.68-1.7
=-2. 40
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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1
1
$$2 * \frac{7}{10}* \frac{7}{10}- 2.4 * \frac{7}{10}- 1.7$$

= $$\frac{49}{50} - 2.4 * 10 *\frac{7}{10 * 10}- 1.7 * \frac{10}{10}$$

= $$\frac{49}{50} - 24 *\frac{7}{100}- \frac{17}{10}$$

= $$\frac{49}{50} - \frac{42}{25} - \frac{17}{10}$$

=$$\frac{98-168-170}{100}$$

= -2.4
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Quote:

What is the value of $$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$ ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

Substituting 0.7 for x, we have:

2(0.7)^2 - 2.4(0.7) - 1.7

2(0.49) - 1.68 - 1.7 = 0.98 - 1.68 - 1.7 = -2.4

Alternate Solution:

Let’s factor the expression 2x^2 - 2.4x - 1.7:

2x^2 - 2.4x - 1.7 = (x - 1.7)(2x + 1)

Now, substituting x = 0.7 in the factored expression, we get (0.7 - 1.7)(2(0.7) + 1) = (-1)(1.4 + 1) = -2.4.

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Joined: 27 Apr 2015
Posts: 39
GMAT 1: 370 Q29 V13 Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Bunuel wrote:
The Official Guide For GMAT® Quantitative Review, 2ND Edition

What is the value of $$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$ ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

Problem Solving
Question: 121
Category: Algebra Simplifying algebraic expressions
Page: 77
Difficulty: 600

GMAT Club is introducing a new project: The Official Guide For GMAT® Quantitative Review, 2ND Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide For GMAT® Quantitative Review, 2ND Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!

2x^2-2.4x-1.7
=> x(2x-2.4)+1.7
=> substituting x=0.7
=> 0.7(2*0.7-2.4)+1.7
=> 0.7(1.4-2.4)+1.7
=> 0.7(-1)+1.7
=> -0.7-1.7
=> -2.4

Therefore 'D'

Thanks
Dinesh
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Bunuel wrote:
What is the value of $$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$ ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

$$2x^2 - 2.4x - 1.7$$, substitute x = 0.7

0.7 ( 1.4 - 2.4) - 1.7
-0.7 - 1.7
-2.40

D
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Senior Manager  G
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GMAT 1: 610 Q43 V31 GMAT 2: 640 Q45 V32 GMAT 3: 640 Q47 V31 What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Gentlemen,

$$2x^2-2.4x-1.4 = (x-1.7)(x+0.5) = (0.7-1.7)(0.7+0.5) = -1.0 * 1.2 = -1.2$$

Where is my mistake?
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Bunuel wrote:
What is the value of $$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$ ?

(A) -0.72
(B) -1.42
(C) -1.98
(D) -2.40
(E) -2.89

Problem Solving
Question: 121
Category: Algebra Simplifying algebraic expressions
Page: 77
Difficulty: 600

The Official Guide For GMAT® Quantitative Review, 2ND Edition

Asked: What is the value of $$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$ ?

$$2x^2 - 2.4x - 1.7$$ for $$x = 0.7$$
= 2(.7)^2 - 2.4(.7) - 1.7
=2*.49 - 2.4*.7 - 1.7
= .98 - 1.68 - 1.7
= -.7 - 1.7
= - 2.4

IMO D
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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mykrasovski wrote:
Gentlemen,

$$2x^2-2.4x-1.4 = (x-1.7)(x+0.5) = (0.7-1.7)(0.7+0.5) = -1.0 * 1.2 = -1.2$$

Where is my mistake?

mykrasovski

You factorisation is incorrect. In fact, there is no need for factorisation of the expression.
$$2x^2-2.4x-1.4 \neq (x-1.7)(x+0.5)$$
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GMAT 1: 610 Q43 V31 GMAT 2: 640 Q45 V32 GMAT 3: 640 Q47 V31 Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?  [#permalink]

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Kinshook correct, thanks for the remark. I do not really know what I was thinking when trying to factorize the expression....  Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ?   [#permalink] 15 Sep 2019, 10:44
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