Basic Maths formulaes

Arithmetic / Properties of Numbers

Even/odd (e/o) identities:

1. e +/- e = e
2. e +/- o = o
3. o +/- e = o
4. o +/- o = e
5. e x e = e
6. e x o = e (also: o x e = e)
7. o x o = o

Decimal conversions:

1. ½ = .5
2. 1/3 = .33, 2/3 = .67
3. ¼ = .25, ¾ = .75
4. 1/5 = .2, 2/5 = .4, 3/5 = .6, 4/5 = .8
5. 1/9 = .11 (repeating), 2/9 = .22 (repeating), etc.
6. It’s handy to know 6ths, 7ths, and 8^ths, but they require more memorization and don’t come up as often.

Percent conversions:

1. 37% = 0.37 = 37/100
2. 0.2% = 0.002 = 0.2/100 = 2/1000

Exponents: (note: x^y = “x raised to the y power”)

1. x^-y = 1/x^y
2. (x^y)(x^z) = x^(y+z)
3. (x^y)^z = x^(yz)
4. x^1/2 = radical (square root of) x.

Radicals (roots): (note: r2 = “radical 2” or “square root of 2”)

1. r2 = approximately 1.4
2. r3 = approximately 1.7
3. Know the square of every integer up to 13.
4. r(xy) = r(x) times r(y)

Geometry

Area

1. Triangle: ½ times base times height
2. Rectangle: length times width
3. Circle: pi(r^2)

Circumference:

1. Circle: 2pi(r)
2. All other figures: the sum of the lengths of all sides

Right triangles:

1. a^2 + b^2 = c^2, where a and b are two sides of the triangle and c is the hypotenuse (Pythagorean theorem)2.Common integer solutions to the Pythagorean Theorem, including 3 : 4 : 5, 6 : 8 : 10 (and all other multiples of 3 : 4 : 5), and 5 : 12 : 13
2. The ratio of sides in a triangle with angles 30 : 60 : 90 is x : x(r3) : 2x
3. The ratio of sides in a triangle with angles 45 : 45 : 90 is x : x : x(r2)

Solids:

1. Volume: area of the base times height
2. Surface area: the sum of the areas of all faces of the solid

Coordinate Geometry:

1. Slope of a line = (change in y)/(change in x)
2. Equation of a line: y = mx + b, where m = slope and b = y-intercept (the point at which x = 0)

Miscellaneous

1. Rate = distance/time
2. Combined work: 1/a + 1/b = 1/t, where a and b are the amount of time it takes two entities working alone to complete a task and t is the amount of time it would take them to complete the task working together. (I’ll go into this in more detail, including some shortcuts, in a future Tip.)
3. Average = sum of terms / number of terms
4. Probability = number of desired outcomes / number of possible outcomes

Probability

1. If there are x people and x seats then total

x!

2. If x people and x seats in a cirlce then total

(x-1)!

3. If x person, x seats, d duplicates, then total

x! / d!

4. If 3 men to be chosen from 8 men then 8C3

5. If x people and y seats, and order matters(permutation) ==> xPy

1. ⁿP_n = n!

2. ⁿC_n = 1

3. ⁿC_r = ⁿC_n-r (symmetrical property)

4. ⁿC₁ = n

5. ⁿP₁ = n

6.  nCr = n! / (r!)(n-r)!

7. nPr = n!/(n-r)!

8.

GMAT prep

http://www.urch.com/forums/usercp.php
mtwinkle/chefdevoir

http://beatthegmat.blogspot.com/2005/08/debriefing-from-guy-who-scored-790.html

Manhattan GMAT’s Sentence Correction Guide.

http://englishplus.com/grammar/contents.htm

magazines
http://www.mckinseyquarterly.com
editorial section of the Wall Street Journal

http://www.urch.com/forums/gmat-awa/11608-magic-template.html
http://daveformba.blogspot.com/
http://uniqpath.blogspot.com/search/label/mbaguide
http://daveformba.blogspot.com/2005/01/application-essay-advice.html

Essay topics
http://www.findscore.com/twe/gmat.html
http://www.west.net/~stewart/gmat/qa_3.htm
http://www.west.net/~stewart/ws/wsres.htm
http://www.800score.com/sample-gmat-essay.html