# GRE_Math_.txt

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1. Area of a triangle
1/2 (base)(height)
2. Special Right Traingles
• 3-4-5 (or any multiple of); right triangle; given any 2-find 3rd side length
• 30-60-90; side ratio of X:Xsqrt(3):2X
• 5-12-13 (or any multiple of); right triangle;given any 2-find 3rd side length
• 45-45-90; side ratio of X:X:Xsqrt(2)
3. Circumference of a circle
2(pi)r
4. Arclength
If n is a degree measure-

• S= 1(n/360)(2pi(r))
• S=(ratio of degree part:whole)(circumference)
5. Area of a circle
(pi)r^2
6. Area of a circular sector
If n is the degree measue of the sector's central angle-

• A= 1(n/360)(pi(r^2))
• A=(ratio of degree of sector:degree of circle)(area of circle)
7. Interior Angles of a polygon
The sum of the interior angles of a polygon= (n-2)(180), where n is the number of sides
8. Surface area of a rectangular solid
2lw+2wh+2lh
9. Volume of a rectangular solid
• solid =lwh
• cube =(=l^3)
10. Volume of a cylinder
(pi)(r^2)(h)
11. Percent formula
Part= (perecnt)(whole)
12. Probability
Favorable/Possible
13. Solving an inequality
When multiplying or dividing both sides by a negative number you must reverse the sign
14. Midpoint between
(x1, y1), (x2, y2)
= [(x1+x2)/2], [(y1+y2)/2]
15. Divisible by 2
If last digit is divisible by 2
16. Divisible by 3
If the SUM of its digits is divisible by 3
17. Divisible by 4
If last two digits are divisble by 4
18. Divisible by 5
Ends in 0 or 5
19. Divisible by 6
If it is divisible by both 2 (last two digists divisible by 2) and 3 (SUM of its digits is divisble by 3)
20. Divisible by 9
If the SUM of its digits is divisible by 9
21. First 25 primes (<100)
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97
22. complimentary lines
make up a right angle
23. supplementary lines
make up a straight line
24. Ratio of areas of two similar triangles
square of the ratio of corresponding lengths

(if triangle b is twice the size of triangle a, (2/1)^2=4; 4 times the area of triangle a)
25. Special right traingle side length ratios
1:1:(sqrt)2 -isosceles right triangles

1:(sqrt)3:2 -30-60-90 triangle
26. pythagorean triplets
3,4,5 (and any multiple of these e.g., 6,8,10)

5,12,13 (and any multiple of these)
27. Surface area of a cylinder
• A=(circumfrence of circular base)(height)+(2area of circular bases)
• A=[(2pi(r)h)] + [2(pi)r^2)]
28. The diagonal through a box
d^2=(l^2)+(w^2)+(h^2)
29. Area of a trapeziod
1/2(b1+b2)(h)
30. Counting Principle
-two tsks; N ways to do/choices for the first and M was to do/choices for the second
• (NM)
• Use anytime a question asks, "how many" (ways to do..., numbers between..., arrangments of...)
31. Probability an experiment will replicate
• (probability of first event)(probability of second)(...)...
• [ex; coin landing heads 3x in a row; (1/2)(1/2)(1/2)=1/8]
32. Probability of E and F occurring
• Independent: p(E and F) = p(E) x p(F)
• Dependent: p(E and F) = p(E) x p(FlE)
• Conditional: p(FlE) = p(E and F)/p(E)
• 0 if mutually exclusive
33. Probability of E or F occurring
• p(E)+p(F) - p(E and F)
• If mutually exclusive: p(E)+p(F)
34. Common factorials
• 0!=1
• 1!=1
• 2!=2
• 3!=6
• 4!=24
• 5!=120
• 6!=5040
35. Permutation (without replacement) (nPr)
(ways to select officers)
• The number of ways of obtaining an ordered subset of elements from a set of elements is given by
• nPr=n!/(n-r)!
36. Permutation (with replacement) (nPr)
"permutation lock"
n^r
37. Combination (without order) (nCr)
• Number of combinations of n distict objects taken r at a time
• n!/[r!(n-r)!] = nPr/r!
 Author: ghstechnology ID: 82464 Card Set: GRE_Math_.txt Updated: 2011-04-28 12:34:28 Tags: math Folders: Description: math Show Answers: