Lesson: General GMAT Math Strategies

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GMAT practice question (difficulty level: 650 to 800) – Veritas Prep--- this is a good question!
gmat-admin's picture

I agree. Lots of different ways to solve that question.

If I do not know how many pairs of 65, but I know for sure that the fourth digital of their sum must be 0 or 5, so the only choice E 1365.
gmat-admin's picture

Perfect reasoning!

Hi Brent,
I found these SC flash cards. https://www.slideshare.net/GMATPrepNow_free/interactive-sentence-correction-flashcards-by-gmat-prep-now

Amazing work!!! Is there another for Math section? Need one for my last day preparations.
Thanks
gmat-admin's picture

We have GMAT Math flashcards here: https://www.slideshare.net/GMATPrepNow_free/gmat-math-flashcards

Cheers,
Brent

Thanks! very helpful!

Hello Brent,

Can you help with the following question please! Thanks

(-1.9)(0.6) – (2.6)(1.2))/6.0 = ?

A) -0.71

B) 1.00

C) 1.07

D) 1.71

E) 2.71
gmat-admin's picture

You bet!

We can apply the halving-doubling strategy (explained here: https://www.gmatprepnow.com/module/general-gmat-strategies/video/1113)

Let's deal with the NUMERATOR first.

Applying the halving-doubling strategy, we can write the following:
(2.6)(1.2) = (5.2)(0.6)

So, we get: (-1.9)(0.6) – (2.6)(1.2) = (-1.9)(0.6) – (5.2)(0.6)
= 0.6(-1.9 - 5.2) [I factored out the 0.6]
= 0.6(-7.1)

Now the ENTIRE FRACTION....
(-1.9)(0.6) – (2.6)(1.2))/6.0 = (0.6)(-7.1)/(6.0)
= (0.6/6.0)(-7.1)
= (1/10)(-7.1)
= -0.71

Cheers,
Brent

gmat-admin's picture

Now comes the 10-second solution!

When we scan the answer choices (ALWAYS scan the answer choice before performing any calculations), we see that only one answer choice is NEGATIVE (hmmmm!!!)

In the numerator we have: (-1.9)(0.6) – (2.6)(1.2)
(-1.9)(0.6) is NEGATIVE
And (2.6)(1.2) is POSITIVE

So, (-1.9)(0.6) – (2.6)(1.2) = NEGATIVE - POSITIVE
= NEGATIVE
So, the numerator is some NEGATIVE number

The denominator (6) is a POSITIVE number

So, the entire fraction becomes NEGATIVE/POSITIVE, which evaluates to be NEGATIVE.
In other words, the entire fraction has a NEGATIVE value

Since answer choice A is the only NEGATIVE answer choice, it must be the correct answer.

Cheers,
Brent

Thank you so much. this video makes me feel relieved :)


gmat-admin's picture

Glad to hear that!

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