# GMAT Math Prep

## Terms

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What is the formula for percent change?
% Change = Difference/0riginal
For a percent increase or decrease calculation, how do you determine what the orginal number is?
For percent increase, the amount of the original is the smaller number. For percent decrease, it's the larger number
Data Sufficiency -
What do A, B, C, D, E mean?
(A) means 1 works and 2 doesn't;

(B) means 2 works and 1 doesn't;

(C) means neither works by itself but they work together;

(D) means each works by itself; and

(E) means you just don't have enough information to answer the question
Data Sufficiency: What are the shortcut definitions for ABCDE?
(A) = (1) only
(B) = (2) only
(C) = Combination
(D) = inDependence
(E) = Extraneous
Data Sufficiency - What is the strategy?
Always write AD/BCE before you start a Data Sufficiency question.
Dividing Decimals: How do you solve 2.8/0.04?
Move the decimal point in the denominator as far to the right as necessary to make it an integer. Then move the decimal in the numerator the same number of places to the right. Divide normally.
2.8/0.04 = 280/4 = 70.
An integer is divisible by 2 whenever...
An integer is divisible by two whenever its last digit is divisible by 2.
An integer is the divisible by 3 whenever...
An integer is the divisible by 3 whenever the sum of its digits is also a multiple of 3.
An integer is divisble by 4 whenever ...
An integer is divisble by 4 whenever its last two digits, taken as a two-digit number, is divisible by 4.
An integer is divisible by 5 whenever...
An integer is divisible by 5 whenever its last digit is either a 5 or a 0.
An integer is divisible by 6 whenever...
An integer is divisible by 6 whenever it's divisible by both 2 and 3, since 6's prime factorization is
2 * 3.
An integer is divisible by 9 whenever...
An integer is divisible by 9 whenever the sum of its digits is also a multiple of 9.
An integer is divisible by 10 whenever...
An integer is divisible by 10 whenever it ends in a 0.
Adding or Subtracting Fractions - use the Bowtie method for:
3/5 + 1/4
Bowtie method:
1. Multiply the individual denominators together to get the denominator of the answer. (5 * 4 = 20)

2. Multiply 4 (the denominator of the second fraction) by 3 (the numerator of the first fraction). Put that number on top of the first fraction. Repeat the same step on the other side. Multiply 5 by 1. Put a five on top of the second fraction.

3. Add the numbers to find the numerator. (12 + 5 = 17.) That's the numerator of the answer. 20 is the denominator.

4. Reduce if possible. Here you can't. 17 is prime.

Mutliply: 5.2 x 0.2
5.2 x 0.2 becomes 52 x 2 = 104

Count the number of decimal places in the original numbers. 5.2 and 0.2 contain one decimal place each, for a total of two. This translates to the number of decimal places in the final answer, which becomes 1.04
How do you convert percent to a fraction
To convert a percent to a fraction, just place the percent over a denominator of 100:
65% = 65/100
To convert a percent to a decimal...
To convert a percent to a decimal, just move the decimal point two places to the left:
65% = 0.65
By itself, a ratio tells you only...
A ratio tells you the relative amount of each item. It does not tell you the actual amounts.
You can find a fractional part from a ratio, which means you can also find a ________, but you cannot find _____________
"Percentage"
"the actual amounts"
In a ratio, all you need is ______in addition to the ratio
"one actual number"
Set up the % translation box for word problems...

See picture
Data Sufficieny: What do you do if Statement (1) solves?

If Statement (1) solves
⬢ Eliminate BCE.
⬢ If Statement (1) solves, but Statement (2) doesn't, (A) is the answer.
⬢ If Statement (1) and Statement (2) both solve, then (D) is the answer.
Data Sufficieny: What do you do if Statement (1) DOES NOT solve?

If Statement (1) doesn't solve
⬢ If Statement (2) solves, (B) is the answer.
⬢ If neither Statement (1) nor Statement (2) solves, but TOGETHER they do solve, the answer is (C).
⬢ If no combination of the Statements solves, then the answer is (E).
In a club with 35 members, the ratio of men to women is 2 to 3 among the members. How many men belong to the club?
Set up a ratio Table.
Ratio Multiplier Actual
Men 2
Women 3
Total 35

First: Add down the first column. 2 + 3 = 5.
Second: Determine the multiplier. To do this, divide the actual number by the ratio number. 35 divided by 5 is 7.
Record this under the multiplier column. Your multiplier is a constant, so the same number should be entered all the way down the column.

Ratio Multiplier Actual
Men 2 7 14
Women 3 7 21
Total 5 7 35
Set up a number showing thousands, hundreds, tens, ones, tenths, hundredths, thousandths
3,125.079

3 = thousands
1 = hundreds
2 = tens
5 = ones
0 = tenths
7 = hundredths
9 = thousandths

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