Math Techniques Flashcards
GCF and LCM
- Prime Factor
- Create box with all unique factors across top, two rows (one for each number)
- Input unique factors with correct exponents
4a. GCF - Multiply lowest values in each column
4b. LCM - Multiply highest values in each column
Converting Decimal to a Fraction
Place the number over 1*10^number of digits in the number.
.123 = 123/1000
Arc Length Calculation
Inner angle / 360 = arc length / circumference
Disguised 3-4-5 Right Triangle
30-40-50
60-80-100
Etc.
Sides-to-Degrees Calculation
(n-2)(180)
Where n is the number of sides of the shape
Combining Ratios
Combine ratios by multiplying or dividing common elements of the two ratios to get a common factor or multiple.
A:B = 5:6
B:C = 8:9
A:C = 2:3
Is x prime?
Test divisibility rules on primes less than square root
Area of an Equilateral Triangle
(√3 / 4)(side^2)
x + y Divisibility
If x and y are both divisible by d, then (x + y) is divisible by d
Negative Exponents
Turns the base into a reciprocal, does NOT change the sign of the base.
1 / 2^(-3) = 2^3
2^(-5) = 1 / 2^(5)
Mixed Roots
Can compare size / manipulate by multiplying to square of coefficient, then moving coefficient under the root.
2√13 = (√4)(√13) = √4*13 = √52
Parallel Symbol
A ∥ B
Standard Deviation
Never need to calculate
- Larger spaces = wider standard deviation
- All constituents of a set shifted by the same interval? No change to standard deviation
Normal Distribution
1st St. Dev = ~34% on either side
2st St. Dev = ~14% on top of 1st St. Dev
3st St. Dev = ~2% on top of 2st St. Dev
Terminating Decimals
Factor out 2s and 5s in denominator - any other factors and it will not terminate
Functions f(x)
Just plug and play
f(x) = x^2 and g(x) = x+3
f(g(1)) = 16
Rectangle
A square is a rectangle, but a rectangle is not necessarily a square. Length is defined as the longer side.
x^2 = 9
x = 3 OR -3
Circumference of a Circle
2πr
Colinear
Two points that lie on the same straight line. Any two points are colinear, three points may or may not be colinear.
Rate / Time Problems
Going opposite directions? Add rates. Then plug into R*T = D
Going the same direction? Subtract rates
Multiplying Decimals
Multiply the decimals by 10^x and then pull back out when finished. Can do with fractions as well.
Simplifying Factorials
9! / 6! = (9)(8)(7)(6!) / 6! = (9)(8)(7)
Can’t do the math? Shouldn’t do the math?
- Estimate
- Backsolve
- Use your own numbers
- Get creative
(w / x) / (y / z)
(w / x)(z / y)
Distance Formula
Rate * Time = Distance
Adding or Subtracting Exponents
23^13 - 23^12
Can ONLY factor, cannot subtract because these are not like terms
(23^12)(23-1) = (23^12)(22)
Percentages
is / of = % / 100
Set equal to each other and cross multiply
Right Triangle
a^2 + b^2 = c^2 applies
“Legs” are the shorter sides, not the hypotenuse
Percent Change
(New - Old) / Old
Semi-circles
If you take any point on a semicircle’s curved edge and draw lines to the corner points, it creates a 90 degree right triangle, with the diameter as the hypotenuse
If a is divisible by b, and b is divisible by c…
a is also divisible by c
If d has e and f as prime factors, then…
d is divisible by e, f, and (e)(f)
Every factor of a number (except 1)…
Is a product of a different combination of the number’s prime factors
Quadrilateral
360 degrees
Area of a Trapezoid = ((Base 1 + Base 2) / 2 )(Height)
Data Sufficiency Answers
A: Only I is sufficient
B: Only II is sufficient
C: I and II are only sufficient TOGETHER
D: I and II are both sufficient ALONE
E: I and II are NOT sufficient TOGETHER
Divisibility Rules: 4
If the final two digits of a number are themselves divisibly by 4, then the number is divisible by 4. 104, 288, 312
Is Zero negative or positive?
Neither - it is a neutral integer
Area of a circle
πr^2
3D Boxes
Vertices = Corners
Faces = Sides
Split into planes to find area, volume, etc.
Simple Permutations
How many ways can n items be ordered? n!
Repeat entities? Divide n by # of repeats (x repeats, divide by x!) 3 repeats? Divide by 3!, or 6
Sum of Consecutive Numbers
(n/2)(First number + Last Number)
Exponent Rules (Addition or Subtraction)
Bases (even if the same) cannot be added or subtracted if the exponent values are different, because they are not like terms. Can factor out the bases though.
Adding or Subtracting Fractions
Simply multiple the denominators to get a common denominator and the numerators accordingly to get add or subtract.
Percentage Change Calculation
(New - Old) / Old
Three Overlapping Sets
Draw Venn Diagram, always subtract out center groups
Arc Length Formula
(Center Angle / 360) = (Arc Length / Circumference)
Divisibility Rules: 6
Must be divisible by 2 and 3
Sides of a 45-degree right triangle
x, x, x√2
Range
Largest value in a set minus the smallest value
Exterior Angles
Sum of opposite interior angles in a triangle is equal to the exterior angle opposite the third angle - look at flash card for diagram
Parallelogram
A shape consisting of two sets of parallel lines, angles opposite each other are equal. Area = base*height
Divisor
All the factors of a number and their negative counterparts
(√x)(√y) =
√xy
(√x) / (√y) =
√(x/y)
√x + √x =
2√x
√x + √y =
Nothing can be done to simplify here
(a / b)(c / d) =
ac/bd
The b root of x^a =
x^(a/b)
Inequalities
When dividing or multiplying by a negative number, the sign flips - may have to test multiple scenarios! All other operations by negatives, or positives do not flip sign
Area of a Triangle
1/2 * base * height
Compounded Percents
Calculate as several percent changes at a time
5-12-13 Right Triangle
May be disguised by proportional multiples
Divisibility Rules: 2
Any even number is divisible by 2
Trapezoids
Area of a trapezoid = ((Base 1 + Base 2)) / 2) * Height
Addition Method
Multiply an equation within a system of equations to get rid of one of the variables, then can add together to solve for the other variable
Can also subtract! Same effect
Substitution Method
For solving systems of equations. Solve for one variable in terms of the other, then plug the result into the other equation
Even Exponent?
The solution to x^2 = 9 could be 3, OR -3
Quant Problem Solving Strategies
- Estimate
- Backsolve
- Use Your Own Numbers
Sum of Equally Spaced Numbers
(Avg. of #s)(# of #s)
(Avg. of #s) = (Biggest + Smallest) / 2
(# of #s) = (Biggest - Smallest) / Spacing
Negative to positive? Cancel out corresponding additions on either side - -23 + 23 = 0, for instance
Favorite Probability Trick
Find the probability of what you’re NOT supposed to be solving for, and subtract it from 1
Data Sufficiency Danger Areas
- Negative Numbers
- Even Exponents
- Non-Integers
- Inequalities with Variables - don’t know sign, may not know direction of inequality symbol