The GMAT Pill Study Method

Ugly Mixture Problem – GMAT Quant Prep

TheGMATPill — Wed, 10 Mar 2010 16:11:29 +0000

A certain shade of gray paint is obtained by mixing 3 parts of white paint with 5 parts of black paint. If 2 gallons of the mixture is needed and the individual colors can be purchased only in one-gallon or half- gallon cans, what is the least amount of paint, in gallons, that must be purchased in order to measure out the portions needed for the mixture?

(A) 2
(B) 2 1/2
(C) 3
(D) 3 1/2
(E) 4

Answer is B. Let me walk you through.

This is a mixture problem.

Step 1) "A certain shade of gray paint is obtained by mixing 3 parts of white paint with 5 parts of black paint. "

You should think: 3 parts white, 5 parts black. That means total there’s 8 parts.

More specifically, 3/8 of the mixture is white stuff and 5/8 of the mixture is black stuff.

Step 2) "If 2 gallons of the mixture is needed and the individual colors can be purchased only in one-gallon or half- gallon cans"

OK. So we know the mixture 2 gallons. How much of these 2 gallons is white stuff and how much of these 2 gallons is black stuff? Of course the white and black stuff must add up to equal 2 gallons.

Well, we know 3/8 of the mixture is white stuff. And the entire mixture is 2 gallons.

So 3/8 of the 2 gallons = 3/8 * 2 = 6/8 = 3/4 = .75 of a gallon is white stuff

Likewise 5/8 of the 2 gallons or 5/8 * 2 = 10/8 = 5/4 = 1.25 of the gallon is black stuff

Step 3) " individual colors can be purchased only in one-gallon or half- gallon cans"

What does this mean? Well, it means that the .75 needs to be rounded up to 1 gallon

And it means the 1.25 gallon needs to be rounded up to 1.5 gallons (a 1 gallon tank and a half gallon tank)

Combine the 1 gallon of white + 1.5 gallon of black = 2.5 total gallons = Answer (B) !!!

Hope that helps!

GMAT Prep: SC question in 15 seconds

TheGMATPill — Thu, 04 Mar 2010 15:36:56 +0000

Displays of the aurora borealis, or “northern lights,” can heat the atmosphere over the arctic enough to affect the trajectories of ballistic missiles, induce electric currents that can cause blackouts in some areas and corrosion in north-south pipelines.

(A) to affect the trajectories of ballistic missiles, induce
(B) that the trajectories of ballistic missiles are affected, induce
(C) that it affects the trajectories of ballistic missiles, induces
(D) that the trajectories of ballistic missiles are affected and induces
(E) to affect the trajectories of ballistic missiles and induce

I arrived at answer E in about 15 seconds, surprisingly. Here’s what went through my head:
I saw the underlined comma in “missiles, induce” and the verb earlier on was “can affect the trajectory”
Immediately, I considered in my head that the answer is one of those -ING options like this:

Alternative #1:
“Displays of the aurora borealis, or “northern lights,” can heat the atmosphere over the arctic enough to affect the trajectories of ballistic missiles, inducing electric currents that can cause blackouts in some areas and corrosion in north-south pipelines.”

which can also be rewritten like this according to framework #3:

” Inducing electric currents that can cause blackouts in some areas and corrosion in north-south pipelines, displays of the aurora borealis, or “northern lights,” can heat the atmosphere over the arctic enough to affect the trajectories of ballistic missiles,.”

But I did not see any -ING versions of INDUCING in the answer choices as I quickly skimmed down the right side of the anwer choices.

Alternative #2:
The next alternative I considered was using the “and” conjunction. The first verb as we noted before was “can heat.” So naturally that should be followed like this:
“can affect X and induce Y”

This second alternative is simple and clear–and it is answer choice (E).

Prepare For Your GMAT

TheGMATPill — Fri, 26 Feb 2010 23:05:09 +0000

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