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What is a Fraction?
part/whole
Fractions: What is the Numerator, Denominator, and the Reciprocal?
-Numerator is the Top
-Denominator is the bottom
-Reciprocal is the fraction flipped over.
How do you add or subtract fractions?
To add or subtract fractions, use the Bowtie method.

3/2 + 2/3 = 13/6

Multilpy criss-cross to get the numerator, then multiple the denominators straight across.
How do you multiply or divide fractions?
-To multiple fractions, multiple straight across. 
-To divide fractions, flip the second fraction (reciprocal), and multiple across.
How do you add and subtract decimal numbers?
Always line up the decimal points.
How do you Multiply Decimals?
Ignore the decimal points, multiply the numbers, count the number of decimal places in each of the original decimals, then move the decimal point the same number of places to the left.
How do you Divide Decimals?
Change both decimals into whole numbers. Move the decimal point in the numberator and the denominator the same number of places to the right. This only works when dividing decimals!
Digit Places?
6,493.782

6: thousands
4: hundreds
9: tens
3: units
7: tenths
8: hundredths
2: thousandths
Percent Change
Percent Change = (diff/orig) x 100
Estimating Percents
21120/64000 ≈ 20/60 = 1/3 = 33.3%
Common conversions among Fractions, Decimals, and Percents
1/2 = 0.50 = 50%
1/3 = 0.33 = 33.3%
2/3 = 0.66 = 66.6%
1/4 = 0.25 = 25%
3/4 = 0.75 = 75%
1/5 = 0.20 = 20%
2/5 = 0.40 = 40%
3/5 = 0.60 = 60%
4/5 = 0.80 = 80%
1/6 = 0.166 = 16.6%
1/8 = 0.125 = 12.5%
Probability
- Probability is always between 0 and 1, inclusive.
- Probability: (number of outcomes you want) / (number of total possible outcomes)

Prob(event happens) + Prob(event does not happen) = 1
Simple Interest
(Principal)x(Rate)x(Time)
Compound Interest
Use Simple Interest as a reference and find an amount slightly higher.

principal x (1+r)^t


A = P*(1 + r/n)nt
where...
P = Principal
r = annual interest rate
n = number of times compounded annually
t = time, in years


OG 12, PS, #78, p. 163

Converting word problems into equations
-'percent' means over 100
-'of' means multiply
-'what' means variables (x,y,z)
-'is' , 'are' , 'were' means equals (=)
Must be True
-Plug in numbers for the variables, Eliminate choices that are false.
-Plug in again using different numbers. Choose numbers that will help you eliminate choices. Try weird numbers (0, 1, neg, extreme, fraction).
-Keep plugging away until only one choice remains.
Yes-No Data Sufficiency
-Before you answer the question, determine what a "Yes" and "No" answer means.
-A statement is sufficient if it enables you to answer the question with a definite "YES" OR "NO".
-A statement is insufficient if you can answer the question with a "Yes" AND a "No" - more than one answer is insufficient. Also, if the statement does not provide enough information to determine an answer.
-When plugging in, you must use numbers that fit the rules laid down by the statements.
x of y cards