The word “percent” can be broken into 2 parts: “per-” meaning divided by, and “cent” meaning 100. (Century is 100 years, there are 100 cents in a dollar). So, 35% means 35 divided by 100, or .
Use this to change percents into fractions. To change a percent to a decimal, simply move the decimal point two places to the left (equivalent to dividing by 100). So, 45% would become 0.45[.]
To go from decimal form to percent, do the reverse: 1.24 = 124%.
If you want to know how to change a fraction to a percent, see if you can write it as an equivalent fraction with 100 as the denominator.
, so is 75%.
Note: You can also change the fraction to a decimal and then to a percent.
Now, let’s look at the “common sense” problem proposed at the beginning: What’s 25% of $100?
Let’s change 25% into a decimal (0.25) or a fraction ().
The word of means “multiply” in word problems. So, we have or .
In both cases, the answer is $25. The discount ($100 - $25) would bring the price down to $75.
Exponents are numbers which indicate how many times to perform multiplication of a number by itself.
Here is a list of properties of exponents:
You’ll often be asked to find missing numbers in sequences or to find the pattern and predict the next number. For these problems, just try the operations (addition, subtraction, multiplication, division, and exponents) to determine the pattern.
Example: Find the missing number in the sequence 1, -2, -5, ___, -11.
You’ll notice that to move from the first to the second term, you can subtract 3.
Do this again and you’ll get -5.
One more time and you’ll get -8, the answer.
(Note: do it again and you’ll get -11, confirming you made the right choice).
Example: Find the next term in the sequence 8, 4, 2, 1, ___.
If you try subtraction, you’ll see 8-4 is 4, but 4-4 is 0, so it can’t be subtraction.
Maybe division works:
so gives as the answer.
Mental math is the best way to speed up your test taking. Use estimation to allow problems to be done mentally. You can quickly check your answer to see if it’s reasonable, or you can eliminate wrong answers ahead of time.
Example: What is ? Answer choices:
First, estimate that would be pretty close to . The answer would be , the third answer choice. This is much faster than long multiplication.
When rounding a number, remember this: If the next digit is 5 or higher, round up.
Round 123.456 to the nearest hundredth.
The hundredth digit is 5, so look at the next one: 6.
6 is 5 or higher, so round the hundredth digit up: 5 to 6.
Thus, 123.456 rounds to 123.46[.]
Round the same number (123.456) to the nearest whole number.
3 is in the ones place, so look at the next digit: 4.
It isn’t 5 or higher, so don’t round up. Thus, 123.456 rounds to 123[.]
Word problems scare a lot of people, but fear not! We’ve provided you with a list of operations and the words associated with them that you’ll commonly find in a word problem.
When solving a word problem, it’s very helpful to identify a variable first. The variable is the unknown amount, usually represented by a letter. Let’s look at this word problem:
One third of all the students are left handed. If 20 students are left handed, how many total students are there?
Step 1: Identify the variable. Usually, look at the last part of a word problem to help. In this case, we are looking for total students. Let s = total students.
Step 2: Translate words into math: “One third of all students are left handed” becomes
Step 3: Solve the equation. For this, reference the next section. In this particular case, the answer is s = 60 students.
Note that a constant is any number that is fixed and not “variable”, such as 2 or 10.
It’s important to know that an equation is like a scale, so if you do something to one side of the equation, you should do it to the other side, too, in order to keep it balanced. You can add/subtract/multiply/divide whatever you want from/to both sides of any equation and it’ll still be true.
Example, if x + 5 = 3 is true, and you add 2 to both sides, then x + 7 = 5 is true as well. In this case, adding 2 wasn’t really a wise choice if you wanted to solve the equation (find what x equals).
To solve a linear equation, isolate the variable by performing the inverse operation to both sides of the equation. Here are some examples of this process.
Example: (the inverse operation of “+ 5” is “– 5”, so let’s subtract 5 from both sides.)
and so the left side becomes which is just x. And on the right side, , so that is your answer: .
Example: (The inverse operation of “–3” is “+ 3”, so let’s add 3 to both sides.)
(Subtracting 3 from z and then adding it back gets you right back to z.)
Example: (The inverse operation of is , so divide both sides by 3.)
(y is multiplied by 3 and then divided by 3, so it is unchanged.)
Sometimes, you’ll have a multiplication problem with a fraction, like the example from the word problem:
In these cases, while you can divide both sides by 3, it’s easiest to multiply both sides of the equation by the reciprocal. (Note: )
Example: (The inverse operation of is , so let’s multiply both sides by 8.)