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by GMATGuruNY » Sun Dec 08, 2013 5:00 am
2x² + 5x - 12 = 0
(2x - 3)(x + 4) = 0.

Root 1:
2x-3 = 0
x = 3/2.

Root 2:
x+4 = 0
x = -4.

Difference = 3/2 - (-4) = 3/2 + 8/2 = 11/2.

The correct answer is E.
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by [email protected] » Sun Dec 08, 2013 12:22 pm
Hi shibsriz,

Mitch has correctly explained the factoring/reverseFOIL that this question is based on. As you continue to study, remember that the rules of math do not change. The GMAT will adapt to you and as you perform at higher levels, the program will test you with "twists" on concepts that you already know. FOIL-ing and reverseFOIL-ing rules don't change, even if the "pieces" do.

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by Mathsbuddy » Sun Dec 08, 2013 6:05 pm
2x² + 5x - 12 = 0

I would always try factorising first just as Mitch:
(2x - 3)(x + 4) = 0

However, if you become stuck you can solve any quadratic in the form
ax² + bx + c = 0 using the quadratic formula instead:

x = {-b +- SQRT[b² - 4ac]}/2a

Handy for those equations that don't factorise.
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