GRE_Math_.txt

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Author:
ghstechnology
ID:
82464
Filename:
GRE_Math_.txt
Updated:
2011-04-28 08:34:28
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math
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math
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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!

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