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If x^2 - 3x + k = -30, what is the value of k?

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If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 10 Apr 2018, 06:34
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A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

71% (05:01) correct 29% (01:10) wrong based on 17 sessions

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Re: If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 10 Apr 2018, 09:10
Bunuel wrote:
If x^2 - 3x + k = -30, what is the value of k?

(1) 2 is an element of the solution set of the given equation.
(2) 5 is an element of the solution set of the given equation.


x^2 - 3x + k = -30

we need value of x to find the value of k

from 1:

x=2
we can find the value of k by replacing the value of x in given eq.

sufficient.

from 2:

x=5

we can find the value of k by replacing the value of x in given eq.

sufficient

hence D
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Re: If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 10 Apr 2018, 09:47
x^2 - 3x + k = -30
x^2 - 3x + (k + 30) = 0

sum of roots = 3
product of roots = (k+30)

1) 2 + a = 3 => a = 1.
So, k+30 = 2 => k = 28

2) 5 + b = 3 => b = -2.
So, k + 30 = -10 => k = -40

EIther sufficient.

(D)
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Re: If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 10 Apr 2018, 23:21
(1). We know that 2 is the solution set, hence simply put that in the given equation & "k" can easily be deduced. Hence, SUFFICIENT.

(2). Similarly, this is also SUFFICIENT.

Hence, both are individually self sufficent to asnwer the question. Hence D
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Re: If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 11 Apr 2018, 06:04
1
This one stumped me for awhile and I'm still not 100% sure. I thought for DS questions 1) and 2) are hints for the same answer. But if X=2 then k=-28. But if X=5 then k= -40. Am I calculating this incorrectly?

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Re: If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 11 Apr 2018, 06:07
Don't know lol....
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Re: If x^2 - 3x + k = -30, what is the value of k?  [#permalink]

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New post 11 Apr 2018, 06:08
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Re: If x^2 - 3x + k = -30, what is the value of k?   [#permalink] 11 Apr 2018, 06:08
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If x^2 - 3x + k = -30, what is the value of k?

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