Don’t lose your progress!

We cover every section of the GMAT with in-depth lessons, 5000+ practice questions and realistic practice tests.

Up to 90+ points GMAT score improvement guarantee

The best guarantee you’ll find

Our Premium and Ultimate plans guarantee up to 90+ points score increase or your money back.

Master each section of the test

Comprehensive GMAT prep

We cover every section of the GMAT with in-depth lessons, 5000+ practice questions and realistic practice tests.

Schedule-free studying

Learn on the go

Study whenever and wherever you want with our iOS and Android mobile apps.

The most effective way to study

Personalized GMAT prep, just for you!

Adaptive learning technology focuses on your academic weaknesses.

Plugging In: Basic Technique

Basmati rice costs $$ $(a−b)$$ per kilogram in standard 7 kilogram packages, where $$a\gt b\gt 0$$, and costs $$ $a$$ per kilogram in nonstandard packages. In terms of $$a$$ and $$b$$, what is the lowest possible price of exactly 24 kilograms of Basmati rice, in dollars?
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]]
That's right. The variables in the question and in the answer choices call for __Plugging In__. Use good numbers such as $$a=5$$ and $$b=3$$. Now the question reads as follows: >{color:purple}Basmati rice costs __$2__ per kilogram in standard 7 kilogram packages and __$5__ per kilogram in nonstandard packages. What is the lowest possible price for 24 kilograms of Basmati rice in dollars?{/color} How does it feel now? Probably much better…. Exactly 24 kilograms are made of 3 standard packages of 7 kilograms, plus 3 kilograms, hence >$$ $2\times 21 + $5\times 3 = $57$$ Your goal is __$57__. __Plug In__ $$a=5$$ and $$b=3$$ in the answer choices, and eliminate any answer choice that clearly is not 57. The correct answer is C.
$$24a-3b$$
$$21a-3b$$
$$24a-21b$$
$$21a-21b$$
$$21a-24b$$