Next, you need to find a number that will satisfy the inequality in one of the remaining answer choices but
not the other, so you can determine whether (C) or (D) is your final answer. Looking at our answer
choices, we can see that we will have to think about plugging in something that will eliminate one answer
choice but not the other. Let’s try out x = 4, because it satisfies (C) but not (D). Mammoth Printing
Company would charge $56 for a 4-color poster.
$28 + $7(4) = $56Colossal Printing would also charge $56 for a 4-color poster.
$34 + $5.50(4) = $56Since Mammoth would not charge more to print the poster than Colossal, you can eliminate (C) and
choose (D).
Using different integers got you down to one answer choice on that question. Sometimes, to find the
answer, you may have to plug in several numbers, including weird numbers like –1, 0, 1, , and −.
Weird Numbers
As you may have noticed,
some numbers have
uncommon properties.
Because of this, we plug
them in only under certain
circumstances, usually
when solving- inequalities
- MUST BE problems
The five numbers just mentioned all have special properties. Negatives, fractions, 0, and 1 all behave in
peculiar ways when, for example, they are squared. Don’t forget about them!
Plugging In: Advanced Principles
If there are variables in the answer choices, you should definitely consider Plugging In. However,
sometimes a question will be a Plug In question that doesn’t have variables in the answer choices. It is,
instead, a hidden Plug In question. It will refer to some unknown amount, but never actually give you a
number. So, you’re going to have to make up your own number.
Here’s an example.