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# Math Strategies for Firefighter Exam Study Guide

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Updated on Jun 23, 2011
• Don't work in your head! Use your test book or scratch paper to take notes, draw pictures, and calculate. Although you might think that you can solve math questions more quickly in your head, that's a good way to make mistakes. Write out each step.
• Read a math question in chunks rather than straight through from beginning to end.As you read each chunk, stop to think about what it means and make notes or draw a picture to represent that chunk.
• When you get to the actual question, circle it. This will keep you more focused as you solve the problem.
• Glance at the answer choices for clues. If they are fractions, you probably should do your work in fractions; if they are decimals, you should probably work in decimals. Make a plan of attack to help you solve the problem.
• If a question stumps you, try one of the backdoor approaches explained in the next section. These are particularly useful for solving word problems.
• When you get your answer, reread the circled question to make sure you have answered it. This helps avoid the careless mistake of answering the wrong question.
• Check your work after you get an answer. Test takers get a false sense of security when they get an answer that matches one of the multiple-choice answers. Here are some good ways to check your work if you have time:
• Ask yourself if your answer is reasonable, if it makes sense.
• Plug your answer back into the problem to make sure the problem holds together.
• Do the question a second time, but use a different method.
• Carry your units. If you are working on a problem that involves working with units, carry them through the problem. The units of the problem must work out for the answer to be correct.
• Approximate when appropriate. For example:
• \$5.98 + \$8.97 is a little less than \$15. (Add: \$6 + \$9)
• .9876 × 5.0342 is close to 5. (Multiply: 1 × 5)
• Skip hard questions and come back to them later. Mark them in your test book so you can find them quickly.

### Backdoor Approaches for Answering Questions That Puzzle You

Remember those word problems you dreaded in high school? Many of them are actually easier to solve by backdoor approaches. The two techniques that follow are terrific ways to solve multiple-choice word problems that you don't know how to solve with a straightforward approach. The first technique, nice numbers, is useful when there are unknowns (like x) in the text of the word problem, making the problem too abstract for you. The second technique, working backward, presents a quick way to substitute numeric answer choices back into the problem to see which one works.

### Nice Numbers

1. When a question contains unknowns, like x, plug nice numbers in for the unknowns. A nice number is easy to calculate with and makes sense in the problem, such as 5, 10, 25, or even 1 or 2.
2. Read the question with the nice numbers in place. Then solve it.
3. If the answer choices are all numbers, the choice that matches your answer is the right one.
4. If the answer choices contain unknowns, substitute the same nice numbers into all the answer choices. The choice that matches your answer is the right one. If more than one answer matches, do the problem again with different nice numbers. You will only have to check the answer choices that have already matched.
Example: Judi went shopping with p dollars in her pocket. If the price of shirts was s shirts for d dollars, what is the maximum number of shirts Judi could buy with the money in her pocket?
1. psd

To solve this problem, let's try these nice numbers: p = \$100, s = 2; d = \$25. Now reread it with the numbers in place:

Judi went shopping with \$100 in her pocket. If the price of shirts was 2 shirts for \$25, what is the maximum number of shirts Judi could buy with the money in her pocket?

Since 2 shirts cost \$25, that means that 4 shirts cost \$50, and 8 shirts cost \$100. So your answer is 8. Let's substitute the nice numbers into all 4 answers:

1. 100 × 2 × 25 = 5000

The answer is b, because it is the only one that matches your answer of 8.

### Working Backward

You can frequently solve a word problem by plugging the answer choices back into the text of the problem to see which one fits all the facts stated in the problem. The process is faster than you think because you will probably only have to substitute one or two answers to find the right one.

This approach works only when:

• All of the answer choices are numbers.
• You are asked to find a simple number, not a sum, product, difference, or ratio.

Here's what to do:

1. Look at all the answer choices and begin with one in the middle of the range. For example, if the answers are 14, 8, 20, and 25, begin by plugging 14 into the problem.
2. If your choice doesn't work, eliminate it. Determine if you need a bigger or smaller answer.
3. Plug in one of the remaining choices.
4. If none of the answers work, you may have made a careless error. Begin again or look for your mistake.
Example: Juan ate of the jellybeans. Maria then ate of the remaining jellybeans, which left 10 jellybeans. How many jellybeans were there to begin with?
1. 60
2. 90
3. 120
4. 140

Starting with one of the middle answers, let's assume there were 90 jellybeans to begin with:

Since Juan ate of them, that means he ate 30 ( × 90 = 30), leaving 60 of them (90 – 30 = 60).Maria then ate of the 60 jellybeans, or 45 of them ( × 60 = 45). That leaves 15 jellybeans (60 – 45 = 15).

The problem states that there were 10 jellybeans left, and you wound up with 15 of them. That indicates that you started with too big a number. Thus, 90, 120, and 140 are all wrong! So, let's try 60:

Since Juan ate of them, that means he ate 20 ( × 60 = 20), leaving 40 of them (60 – 20 = 40).Maria then ate of the 40 jellybeans, or 30 of them ( × 40 = 30). That leaves 10 jellybeans (40 – 30 = 10).

The right answer is a, because this result of 10 remaining jellybeans agrees with the problem.

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