Math Rules Flashcards
If starting fraction is <1, adding same # to top and bottom does what to the fraction?
Increases
If starting fraction is >1, adding same # to top and bottom does what to the fraction?
Decreases
a5 * a3
6(6x)
a5 * a3 = a8
6(6x) = 61 * 6x = 61+x
a5/a3
a5/a3 = a2
Divide terms with the same base, subtract exponents
a0
00
a0 = 1
00 = undefined
Anything to the power of 0 = 1, except 0
(a2)4
x-3(x2)4 / x5
(a2)4 = a8
x-3(x2)4 / x5 = x8 / x5x3 = x8 / x8 = 1
Apply two exponents: multiply the exponents
(ab)3
(2-2y2)-3
(ab)3 = a3b3
(2-2y2)-3 = 26/y6 = 64/y6
Applying exponent to a product: apply exponent to each factor
a2/3
a2/3 = 3√a2
If you raise a number to a fractional power, apply two exponents: the numerator as a power, and the denominator as a fractional root
135 + 133
x5+x3
135 + 133 = 133132 + 133 = 133 (132 + 1)
x5+x3 = x3x2+x3 = x3(x2 + 1)
Add or subtract terms with the same base: pull out a common factor
√2
√3
√2 = 1.4
√3 = 1.7
Square root of a number between 0 and 1 is greater or less than the original number?
√0.5
√2/3
Greater than!
√0.5 > 0.5 –> approx. 0.7
√2/3 > 2/3 –> approx. 0.8
√8 * √2
√27/√3
√15 * √12 / √5
√8 * √2 = √8*2 = √16 = 4
√27/√3 = √27/3 = √9 = 3
√15 * √12 / √5 = √(15 * 12)/ 5 = √(3 * 12) = 6
Multiplying square roots: put everything under the root
√32+42
√310+311
√32+42 = √9+16 = √25 = 5
CANNOT BREAK INTO √32+√42, MUST FOLLOW PEMDAS
√310+311 = √310(1+3) = √310 *√4 = (310)1/2 * 2 = 35 * 2
CANNOT COMBINE FURTHER
Percent Change
x2 - x1 / x1
x2 = final value
x1 = initial value
F - O / O
How to multiply decimals
- 02 * 1.4
- 0003 * 40,000
Multiply as if whole #s and count digits to the right of the decimal:
0.02 * 1.4
- Digits to the right of decimal: 3
- 2 * 14 = 28
- Move decimal three digital to the left: 0.028
Move the same # of places left and right and multiply whole numbers:
0.0003 * 40,000
- Move 0.0003 to the right four places (3)
- Move 40,000 to the left four places (4)
- 3*4 = 12
How to divide decimals
0.0045/0.09
Shift decimal same # in numerator and denominator to make whole number:
0.0045/0.09 = 45/900 (and divide from there)
When should I test cases?
Data sufficiency “theory” problem
Problem solving with a must be or could be question
When should I use smart numbers?
Problem solving with variables, fractions or percents
Ratios
When should I work backwards?
Problem-solving with real values in the answers, answer choices represent a single variable in the problem.
(x+y)2
(x+y)2 = x2 + 2xy + y2
(x-y)2
(x-y)2 = x2 - 2xy + y2
(x+y)(x-y)
(x+y)(x-y) = x2-y2
1 +
Total Cost Formula
= Unit Price * Quantity
Profit
Revenue - Cost
Total Earnings
= Wage Rate * Hours Worked
Miles
Miles per Hour * Hours
Miles per Gallon * Gallon
Distance
Work
Rate * Time
Average Rate
Total Distance / Total Time
Average will always be closer to the closer of the two rates than to the faster (because more time spent in the slower rate)
Standard Deviation
How far from the average the data points typically fall
Small SD: set is clustered closely around the average
Large SD: set is spread out widely with some points appearing far from the mean
If every absolute difference from the mean is equal, the SD equals that difference
Set: 0,0,10,10
Mean: 5
Difference from mean: 5,5,5,5
SD: 5
Weighted Average Formula
Only use if you have two data points and relatively easy #
(Component 1)(Weighting 1) + (Component 2)(Weighting 2)…
Weighted Average
Teeter-Totter Method

Consecutive Integers:
How many integers from 14 to 765, inclusive?
Last - First + 1
765-14 + 1 = 752
Consecutive Multiples:
Last-First / Increment + 1
How many multiples of 7 between 10 and 80?
7 is not a factor of 10 nor 80, so find least multiple and greatest multiple of 7 in that range, and use at 1 and last digit:
(14, 77)
Last-First/Increment + 1
77-14/7 + 1 = 10
Properties of evenly spaced sets:
Average = Median
Average = (First + Last)/2
Total = Avg * # of terms
of terms = [(largest - smallest)/spacing] + 1
Combinatorics
Order doesn’t matter:
Pool!/In!Out!
Order matters:
Pool!/Place!Place!Place!Out!
1st, 2nd, 3rd place, one each, 7 kids total
[7!/1!1!1!4! = 7!6!5!4!/1!1!1!4! = 210 arrangements]
Factor Foundation Rule
If a is a factor of b, and b is a factor of c, then a is a factor of c.
–> If 72 is divisible by 12, then 72 is also divisibly by the factors of 12 (1,2,3,4,6 and 12)
E ± E
O ± O
E ± O
E * E
E * O
O * O
All same, even. One diff, odd.
E ± E = E
O ± O = E
E ± O = O
Any even present, even.
E * E = E
E * O = E
O * O = O
Sum of Two Primes
- All primes are odd except 2
- Prime + Prime will be even unless one of those primes 2 (because O + O, unless 2)
- If problem tells you sum of two primes is odd, one of the primes must be 2, other must not be 2
- If you know 2 cannot be one of the primes in the sum, sum must be even
If one of the sides of a triangle inscribed in a circle is a diameter of the circle, then the triangle must be a ________.
If one of the sides of a triangle inscribed in a circle is a diameter of the circle, then the triangle must be a right triangle.
The angle opposite the diameter is the right angle.
Pythagorean Theorem + Common Right Triangles
a2 + b2 = c2
3 - 4 -5 (32 + 42 = 52) –> 6 - 8 - 10; 9 - 12 - 15; 12 - 16 - 20
5 - 12 - 13 –> 10 - 24 - 26
8 - 15 - 17
Sum of interior angles of a polygon
(n-2) * 180
Triangle (3) = 180
Quadrilateral (4) = 360
Pentagon (5) = 540
Hexagon (6) = 720
Area of a Trapezoid
(base1 + base2)(height) / 2
Area of a Parallelogram
base * height
Triangle Theorem
- Sum of angles = 180
- Angles correspond to opposite sides
- Largest angle is opposite longest side
- Smallest angle is opposite shortest side
- If two sides are equal, their opposite angles are also equal
- Sum of any two sides of a triangle must be greater than the third side
Isosceles Triangle
Two of three sides are equal
Leg: x
Leg: x
Hypotenuse: x√2
Angles: 45/45/90
Equilateral Triangle
Leg opposite 30: x
Leg opposite 60: x√3
Hypotenuse: 2x
Angles: 30/60/90
Exterior Angles of a Triangle

Area of a Triangle
Base * Height / 2
Circumference
Diameter
Area
Circumference: πd OR 2πr
Diameter: 2r
Area: πr2
Area of a Sector
- Find area of entire circle: πr2
- π32 = 9π
- Use central angle to determine what fraction of the entire circle is represented by the sector
- Central angle: 60
- Whole circle: 360
- Fraction: 60/360 –> 1/6 of area –> 1/6 (9π) = 1.5π
Inscribed v Central Angle
Central angle: vertex @ center point of circle
Inscribed angle: vertex on circle itself
An inscribed angle = 1/2 of equivalent central angle
Volume of a Cylinder
V = πr2h
Slope of a line
rise/run = y2-y1/x2-x1
Slope-Intercept Equation
y = mx+b
m = slope
b = y-intercept
Horizontal line: y = #
Verticle line: x = #