C)
D) 0.96tHere’s How to Crack It
This could be a pretty tricky algebra question, but if you read the question carefully and plug in easy
numbers, it will be a breeze.
Let’s start at the beginning. When Erica bought that floor lamp on sale, what did you really wish you
knew? It would be very helpful to start this problem knowing the original price of the floor lamp. So, let’s
start plugging in there. Plug in something you know how to take a percentage of, say 100. Write down
“original = 100” on your scratch paper and move on the next step of the problem. Erica got a 10%
discount, so take 10% of the original price. That means she got a $10 discount, and the discounted price
of her floor lamp was $90. Write that down and move on to the sales tax. If you read carefully, it is clear
that the sales tax is 6% of the discounted price. So, you need to take 6% of the $90 discounted price, or
$5.40. To get her total, add the $5.40 of tax to the $90 for the discounted floor lamp, and you get $95.40.
This is where the careful reading comes in. The variable t in this problem is supposed to be the total
amount she paid, so make sure that you label this on your scratch paper “t = $95.40.”
Next, read the last sentence of the question again, to be sure you know which of the answers is your target
answer. The question asks for the original price of the floor lamp, so circle the number you plugged in for
the original price. Your target answer is 100.
On to the answer choices! When you put $95.40 in for t in (A), you get 99.375. This is not your target
answer, so you can eliminate (A). Choice (B) gives you 91.0116, so that will not work, either. Plugging in
$95.40 into (C) yields the target of 100, so hang on to it while you check (D) just in case. When you plug
in for (D), you get 91.584. Since that does not match your target, you can eliminate (D) and choose (C)!
Which Numbers?
Although you can plug in any number, you can make your life much easier by plugging in “good” numbers
—numbers that are simple to work with or that make the problem easier to manipulate. Picking a small
number, such as 2, will usually make finding the answer easier. If the problem asks for a percentage, plug
in 100. If the problem has to do with minutes, try 30 or 120.
Except in special cases, you should avoid plugging in 0 and 1; these numbers have weird properties.
Using them may allow you to eliminate only one or two choices at a time. You should also avoid plugging
in any number that appears in the question or in any of the answer choices. Using those numbers could
make more than one answer match your target. If more than one answer choice matches your target, plug in
a new number and check those answer choices. You may have to plug in more than once to eliminate all
three incorrect answers.