[Math Revolution GMAT math practice question]
What is the sum of roots of the equation x^2 - 40x + 399 = 0?
A. 19
B. 20
C. 21
D. 40
E. 399
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What is the sum of roots of the equation x^2 – 40x + 399 =
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Max@Math Revolution
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regor60
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x^2-40x+ 399 = (x^2-40x +400) -1 = 0Max@Math Revolution wrote:[Math Revolution GMAT math practice question]
What is the sum of roots of the equation x^2 - 40x + 399 = 0?
A. 19
B. 20
C. 21
D. 40
E. 399
x^2-40x+400 = 1
(x-20)^2 = 1
x-20 = 1 or -1
x=21 and 19
Sum = D, 40
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GMATGuruNY
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For any quadratic in the form x² + bx + c = 0:Max@Math Revolution wrote:[Math Revolution GMAT math practice question]
What is the sum of roots of the equation x^2 - 40x + 399 = 0?
A. 19
B. 20
C. 21
D. 40
E. 399
Sum of the roots = -b.
Product of the roots = c.
In the given quadratic, b = -40.
Thus, the sum of the roots = -b = -(-40) = 40.
The correct answer is D.
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I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
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regor60
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doh!<i class="em em---1"></i>GMATGuruNY wrote:For any quadratic in the form x² + bx + c = 0:Max@Math Revolution wrote:[Math Revolution GMAT math practice question]
What is the sum of roots of the equation x^2 - 40x + 399 = 0?
A. 19
B. 20
C. 21
D. 40
E. 399
Sum of the roots = -b.
Product of the roots = c.
In the given quadratic, b = -40.
Thus, the sum of the roots = -b = -(-40) = 40.
The correct answer is D.
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Max@Math Revolution
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=>
Let p and q be the roots of the equation x^2 - 40x + 399 = 0.
Then x^2 - 40x + 399 = (x-p)(x-q) = x^2 - (p+q)x + pq.
Equating coefficients gives p + q = 40 from the coefficient of x.
Therefore, the answer is D.
Answer: D
Let p and q be the roots of the equation x^2 - 40x + 399 = 0.
Then x^2 - 40x + 399 = (x-p)(x-q) = x^2 - (p+q)x + pq.
Equating coefficients gives p + q = 40 from the coefficient of x.
Therefore, the answer is D.
Answer: D
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Scott@TargetTestPrep
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In a quadratic equation of the form ax^2 + bx + c = 0, the sum of the roots is -b/a. Therefore, here the sum of the roots is -(-40)/1 = 40.Max@Math Revolution wrote:[Math Revolution GMAT math practice question]
What is the sum of roots of the equation x^2 - 40x + 399 = 0?
A. 19
B. 20
C. 21
D. 40
E. 399
Answer: D
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