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

A flock of $$z$$ birds lands on a fig tree. One-fourth of the birds fly away while 5 more birds land on the same tree. In terms of $$z$$, how many birds are now on the tree?
Correct. [[snippet]] When $$z=4$$, this answer choice yields >$$\displaystyle \frac{3z+20}{4} = \frac{3(4)+20}{ 4} = \frac{32}{ 4} = \color{blue}{8}$$, so it matches your *goal*. All other answer choices are eliminated by this Plug-In, so this is the right answer choice. >A) $$\frac{z}{4} + 5 = \frac{4}{4} + 5 =\color{red}{6}$$, which is not equal to your goal of 8. __POE__. >C) $$3z+2 = 3(4)+2 = \color{red}{14}$$, which does not equal to 8. __POE__. >D) $$3z+6$$. This choice is even greater than C. __POE__. >E) $$z+3 = 4+3=\color{red}{7}$$, which is not equal to 8. __POE__.
Incorrect. Notice that $$\frac{1}{4}$$ of the birds fly *away*, while the question asks for how many birds *remain* on the tree. This is exactly the type of careless mistakes that __Plugging In__ helps you avoid. __Plugging In__ good numbers forces you to work out the problem step by step instead of jumping to conclusions based on what you *think* you've read.
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]] Did you try to __Plug In__ $$z=8$$ and get more than one answer choice? In that case, __POE__, then change numbers and __Plug In__ again for the remaining answers only.
$$\frac{z}{4} + 5$$