Math GRE
How do you compute the number of positive divisors?
Find the prime factorization of the number
Take the exponents of the prime factors
Add 1 to each of the exponents
Multiply the exponents + 1
In a normal distribution, which percentage of the population falls within 1 SD under and above the mean?
68%
In a normal distribution, which percentage of the population falls within 2 standard deviations under and above the mean?
95%
In a normal distribution, how do we find the 3rd percentile?
Mean - 2SD
In a normal distribution, how do we find the 16th percentile?
Mean - SD
In a normal distribution, how do we find the 85th percentile?
Mean + SD
In a normal distribution, how do we find the 97th percentile?
Mean + 2 SD
Say four pythagorean triplets that are not multiples of each other
3,4,5
5,12,13
8,15,17
7,24,25
sqrt(2)
1.41
sqrt(3)
1.73
sqrt(5)
2.23
sqrt(6)
2.45
sqrt(7)
2.65
sqrt(8)
2*sqrt(2)=2*1.41=2.82
sqrt(10)
3.16
3^3
27
4^3
64
6^3
216
7^3
343
8^3
512
9^3
729
11^2
121
12^2
144
13^2
169
14^2
196
15^2
225
sqrt(121)
11
sqrt(144)
12
sqrt(169)
13
sqrt(196)
14
sqrt(225)
15
How many multiples of a number between two numbers
(Last − First) ÷ Increment + 1
Multiplier for r anual interest compounding in n periods a year
1+(r/n)
How does the amount earned with compound interest vary when the compounding period decreases its length?
it increases
How are the sides and angles of a triangle related?
The largest side is opposite to the largest angle and the shortest side is opposite to the shortest angle
When is a number divisible by 4?
When it is divisible by 2 twice or when the 2 last digits arw divisible by 4
When is a number divisible by 8?
When it is divisible by 2 three times or when the 3 last digits form a number divisible by 8
What is the average of an evenly spaced set?
(first term + last term)/2
What is the median of a set containing an odd number of values?
The middle number
What is the median of a list containing an odd number of values?
Cannot be determinef
What is the first quartile?
The median of the bottom half of a list
What is the 3rd quartile?
The median of the upper half of a list
Area of a trapezoid
height*(b1+b2)/2
Which, of all quadrilaterals, has the greatest area, given a fixed perimeter?
The square
Which, of all the quadrilaterals with a given area, has the SMALLEST perimeter?
The square
For a given number of sides and a given area, which poligon has the smallest perimeter?
The regular poligon
For a given number of sides and a given perimeter, which poligon has the greatest area?
The regular poligon
How do we maximize the area of a triangle, given 2 sides?
Placing those sides perpendicular to each other (right triangle)
How do we maximize the area of a parallelogram, given 2 sides?
Placing those sides perpendicular to each other -> rectangle
Prime numbers below 60
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59
Which numbers to pick for QC?
ZONEF
Zero
One
Negative
Extremes
Fractions
2^4
16
2^5
32
2^6
64
2^7
128
2^8
256
2^9
512
2^10
1024