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

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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(7)(7)-24(7)-170]/100
=-2.4
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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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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Kudos
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]
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

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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]
[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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Kudos
$$2 * \frac{7}{10}* \frac{7}{10}- 2.4 * \frac{7}{10}- 1.7$$

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

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

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

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

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

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

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

Or, $$2x^2 - 3.4x + x - 1.7$$

Or, $$2x (x - 1.7) + 1(x - 1.7)$$

Or, $$(x - 1.7)(2x + 1)$$

Or, $$(0.7 - 1.7)(2*0.7 + 1)$$

Or, $$(-1)(2.14)$$

Or, $$-2.40$$, Answer must be (D)
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Re: What is the value of 2x^2 - 2.4x - 1.7 for x = 0.7 ? [#permalink]
To find the value of the expression 2x^2 - 2.4x - 1.7 for x = 0.7,
Replacing x with 0.7 in the expression:

2(0.7)^2 - 2.4(0.7) - 1.7
Simplifying:
2(0.49) - 1.68 - 1.7
0.98 - 1.68 - 1.7

Combining like terms:
-0.7 - 1.7
-2.4