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555-605 (Medium)|   Algebra|      
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Bunuel
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If (m-8) is a factor of m^2-jm-24, then j= 14 Apr 2017, 04:17
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

Difficulty:

25% (medium)

Question Stats:

71% (00:58) correct 29% (01:15) wrong based on 174 sessions

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If (m - 8) is a factor of m^2 - jm - 24, then j =

A. 3
B. 5
C. 6
D. 11
E. 16
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B
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GMAT Focus 1: 735 Q90 V89 DI81
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If (m-8) is a factor of m^2-jm-24, then j= 14 Apr 2017, 04:55
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Bunuel
If (m - 8) is a factor of m^2 - jm - 24, then j =

A. 3
B. 5
C. 6
D. 11
E. 16
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some theory
\(ax^2+bx+c=0\) is a quadratic equation and relates to a parabola when drawn on graph.
Power 2 can generally be taken as the equation has two values for which the equation will hold true. Ofcourse these two can be same or different or a combination of real and unreal numbers.
SUM of roots here is \(\frac{-b}{a}\)
PRODUCT of roots is \(\frac{c}{a}\)

Now let's apply it to the present Q
m-8 means 8 is one of the roots..
Other values are b=-j ; c=-24 ; a=1
So product of roots = 8*z=-24/1 or Z, the second root, is \(\frac{-24}{8}=-3\)..
SUM= 8+(-3)=-(-j)..... j=5

B
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If (m-8) is a factor of m^2-jm-24, then j= 14 Apr 2017, 07:15
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given equation is quadratic,, so max 2 roots are possible,...

also given m-8 is factor implies m=8 can be subtituted in the equation

hence 8^2 - 8j -24 = 0

solving j = 40/5 = 8

ans B
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If (m-8) is a factor of m^2-jm-24, then j= 14 Apr 2017, 07:51
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Also, substitute the options for j in the equation and we can back-solve to get B?
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If (m-8) is a factor of m^2-jm-24, then j= 23 Apr 2017, 21:30
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chetan2u
Bunuel
If (m - 8) is a factor of m^2 - jm - 24, then j =

A. 3
B. 5
C. 6
D. 11
E. 16


some theory
\(ax^2+bx+c=0\) is a quadratic equation and relates to a parabola when drawn on graph.
Power 2 can generally be taken as the equation has two values for which the equation will hold true. Ofcourse these two can be same or different or a combination of real and unreal numbers.
SUM of roots here is \(\frac{-b}{a}\)
PRODUCT of roots is \(\frac{c}{a}\)

Now let's apply it to the present Q
m-8 means 8 is one of the roots..
Other values are b=-j ; c=-24 ; a=1
So product of roots = 8*z=-24/1 or Z, the second root, is \(\frac{-24}{8}=-3\)..
SUM= 8+(-3)=-(-j)..... j=5

B
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chetan2u - would you recommend knowing the quadratic formula or all GMAT algebra questions solvable through foiling?
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If (m-8) is a factor of m^2-jm-24, then j= 08 Jun 2018, 11:18
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Bunuel
If (m - 8) is a factor of m^2 - jm - 24, then j =

A. 3
B. 5
C. 6
D. 11
E. 16
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Because we know that (m - 8) is a factor, we know that (m - 8) = 0, and so m = 8. We substitute 8 for m into the equation, obtaining:

8^2 - 8j - 24 = 0

40 = 8j

5 = j

Answer: B
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