Hi All,

As you perform at higher levels on the GMAT, the test will throw you questions based on subjects that you know, but in ways that you're probably not used to thinking about. This question is based on Quadratics, but you have to organize the information 'backwards', using an end result to reconstruct the original equation.

We're told that one root of the equation X^2 − 5X + m = 0 is 10. We can now start to reverse-FOIL this equation....

X^2 - 5X + M = 0

(X-10)(X + ?) = 0

Since the sum of the "O" and "I" in foil is -5X, we can set up the following equation:

-10X + ?X = -5X

?X = 5X

This proves that the missing 'number' in the above equation is 5...

(X-10)(X+5) = 0

X^2 - 10X + 5X - 50 = 0

X^2 - 5X - 50 = 0

The question asks for the value of M + 3. Since M = -50, (M+3) = -47.

Final Answer:

GMAT assassins aren't born, they're made,

Rich

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# Rich Cohen

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