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# GMAT Speed Tips

### GMAT Traps

Question | Answer |
---|---|

2^2 | 4 |

2^3 | 8 |

2^4 | 16 |

2^5 | 32 |

2^6 | 64 |

2^7 | 128 |

2^8 | 256 |

2^9 | 512 |

2^10 | 1024 |

1! | 1 |

0! | 1 |

2! | 2 |

3! | 6 |

4! | 24 |

5! | 120 |

6! | 720 |

7! | 5040 |

8! | 40320 |

9! | 362880 |

10! | 3628800 |

0 Squared | Undefined |

1 Squared | 1 |

2 Squared | 4 |

3 Squared | 9 |

4 Squared | 16 |

5 Squared | 25 |

6 Squared | 36 |

7 Squared | 49 |

8 Squared | 64 |

9 Squared | 81 |

10 Squared | 100 |

11 Squared | 121 |

12 Squared | 144 |

13 Squared | 169 |

14 Squared | 196 |

15 Squared | 225 |

16 Squared | 256 |

17 Squared | 289 |

18 Squared | 324 |

19 Squared | 361 |

20 Squared | 400 |

21 Squared | 441 |

22 Squared | 484 |

23 Squared | 529 |

24 Squared | 576 |

25 Squared | 625 |

12 X 1 | 12 |

12 X 2 | 24 |

12 X 3 | 36 |

12 X 4 | 48 |

12 X 5 | 60 |

12 X 6 | 72 |

12 X 7 | 84 |

12 X 8 | 96 |

12 X 9 | 108 |

12 X 11 | 132 |

13 X 2 | 26 |

13 X 3 | 39 |

13 X 4 | 52 |

13 X 5 | 65 |

13 X 6 | 78 |

13 X 7 | 91 |

13 X 8 | 104 |

13 X 9 | 117 |

13 X 11 | 143 |

13 X 12 | 156 |

14 X 2 | 28 |

14 X 3 | 42 |

14 X 4 | 56 |

14 X 5 | 70 |

14 X 6 | 84 |

14 X 7 | 98 |

14 X 8 | 112 |

14 X 9 | 126 |

14 X 11 | 154 |

14 X 12 | 168 |

15 X 4 | 60 |

15 X 5 | 75 |

15 X 6 | 90 |

15 X 7 | 105 |

15 X 8 | 120 |

15 X 9 | 135 |

15 X 11 | 165 |

15 X 12 | 180 |

16 X 2 | 32 |

16 X 3 | 48 |

16 X 4 | 64 |

16 X 5 | 80 |

16 X 6 | 96 |

16 X 7 | 112 |

16 X 8 | 128 |

16 X 9 | 144 |

16 X 10 | 160 |

16 X 11 | 176 |

16 X 12 | 192 |

Y = MX + B | X, Y = Coordinates on the Line M = Slope B = Y Intercept |

X^A + X^B | X^A+B |

RootA X RootB | Root(A X B) |

RootA / RootB | Root(A / B) |

RootA^2 | Absolute Value A |

X% of Y Equals | Y% of X |

Work Formula | T = AB/A+B |

A Root C + B Root C | (A + B) Root C |

Name all the Pythagorean Triplets | 3:4:5 5:12:13 7:24:25 8:15:17 9:40:41 |

Surface Area of a Rectangular Solid | 2(LW+LW+WH) |

Surface Area of a Cylinder | 2 Pie R^2 + 2 Pie R H |

Volume of a Cylinder | Pie R^2 H |

Volume of a Rectangular Solid | LWH |

1/9 | .111 repeating or 11.1% |

1/8 | .125 or 12.5% |

1/7 | .14 or 14% |

1/6 | .166 repeating or 16.6% |

1/5 | .20 or 20% |

1/4 | .25 or 25% |

1/3 | .333 repeating or 33.3% |

1/2 | .50 or 50% |

3/8 | .375 or 37.5% |

2/9 | .222 repeating or 22.2% |

2/7 | .28 or 28% |

3/7 | .42 or 42% |

4/7 | .57 or 57% |

5/7 | .71 or 71% |

6/7 | .85 or 85% |

5/6 | .83 or 83% |

5/8 | .625 or 62.5% |

Why do decimals repeat? | Because they are divided by 9 |

How to convert a repeating decimal to fraction? | Put it over 9. for example .545454 = 54/99 .0787878 = 78/990 |

7/8 | .875 or 87.5% |

1/11 | .0999 repeating or 9% |

1/12 | .083 or 8.3% |

{A} + {B} = {A+B} ONLY when | A*B >=0 otherwise {A} + {B} > {A+B} |

(a+b+c) * (1/a +1/b+1/c) >= | 9 |

For any positive integer N, (1+1/N)^N is >= to what? <= to what? | =>2 and <=3 |

a^2 + b^2 + c^2 >= | ab + bc + ca ... if a=b=c then the case of equality holds true |

a^4+b^4+c^4+d^4 = | 4abcd (equality arises when a=b=c=d=1) |

(n!)^2 > | n^n |

If N is even, n(n+1)(n+2) is divisible by what? | 24 |

x^n - a^n = | x-a will be a multiple of x^n - a^n |

(m + n)! is divisible by | m! * n! |

When a 3 digit # is reversed and the difference is taken of these two #'s, the middle # is always what and sum of other two #'s is always what? | middle number is always 9, sum of other two numbers is 9 |

the sum of the first "n" positive integers = | n(n+1)/2 |

the sum of the squares of first "n" positive integers = | n(n+1)(2n+1)/6 |

the sum of the first "n" even numbers = | n(n+1) |

the sum of the first "n" odd numbers = | n^2 |

If "N" is represented as a^x * b^y * c^z where (a,b,c... are prime) the total # of factors is | (x+1)(y+1)(z+1) |

total number of prime numbers between 1-50 | 15 |

total number of prime numbers between 51-100 | 10 |

total number of prime numbers between 101-200 | 21 |

2^10 = 4^What = 32^what | 2^10 = 4^5= 32^2 |

3^8 = 9^what = 81^what | 3^8 = 9^4 = 81^2 |

7*11*13 = | 1001 |

11*13*17 = | 2431 |

13*17*19 = | 4199 |

19*21*23= | 9177 |

19*23*29= | 12673 |

When the digits of a # are added up and the result is either blank or blank or blank or blank, then what? | the number could be a perfect square if the digits add up to 1 or 4, or 7 or 9 |

To find out the sum of three digit numbers formed with a set of given digits... | (sum of digits) * (# of digits - 1)! * (1 * # of digits, i.e. 3# =111) |

x^n + y^n + z^n will not have a solution if n is >= to | 3 |

What is the only 3 digit number expressed as the sum of factorials of the individual digits? | 145 (1! +4!+ 5!) |

when a number is of the form a^n -b^n then | the # is always divisible by a-b |

Pascals triangle for compounding interest | Number of years 1 - 1 2 - 1 2 1 3 - 1 3 3 1 4 - 1 4 6 4 1 |

Explain pascals triangle for CI given P=1000, R=10%, and N=3 years | 1 * 1000 + 3 *100 + 3*10 + 1*1= 1331 coefficients of each number |

Suppose product is increased by X%, then decreased by Y%, the final change in % is what formula? | X-Y-XY/100 = profit or loss. To find the price sold, the profit or loss % will be multiplied to get 100% to find cost. Add cost plus profit/loss to find selling price |

When the cost price of 2 articles is the same, and % marked up is the same, which one should be assumed as 100? | the marked price |

When P represents principal, R represents rate of interest, then, the difference between 2 years simple interest and compounding is | P * (R/100)^2 |

When P represents principal, R represents rate of interest, then, the difference between 3 years simple interest and compounding is | ((P * R^2)*(300+R))/100^3 |

If A can finish the work in X time and B can finish the same work in Y time, then both can finish the time in - | (X*Y)/(X+Y) time |

If A can finish the work in X time and A+B together can finish the same work in S time, then B can finish the time in - | (XS)/(X-S) time |

If A can finish the work in X time and B in Y time and C in Z time then all of them working together can finish the work in - | (XYZ)/(XY+YZ+XZ) |

If A can finish the work in X time and B in Y time and A+B+C together in S time then C can finish that work alone in - | (XYS)/(XY-SX-SY) |

If A can finish the work in X time and B in Y time and A+B+C together in S time then B+C can finish that work in- | (SX)/(X-S) |

If A can finish the work in X time and B in Y time and A+B+C together in S time then A+C can finish that work in- | (SY)/(Y-S) |

When there are "n" items and "m" out of such items should follow a pattern then the probability is given by | 1/m! i.e. 10 girls dance, one after the other. what is prob. A dance before B before C? n=10, m=3 (A,B,C) 1/3! =1/6 |

For any regular polygon, the sum of exterior angles is = to what? what is measurement of any external angle? | 360 degrees and each angle is 360/n when "n" is # of sides |

For any regular polygon, the sum of interior angles is = to what? what is measurement of any external angle? | (n-2)*180 degrees where "n" is number of sides and measurement of one angle is (n-2)/n*180 |

If any parallelogram can be inscribed in a circle then it must be a | rectangle |

If a trapezium can can be inscribed in a circle, it must be an | isosceles trapezium (oblique sides equal) |

Area of Rhombus = | product of two diagonals |

Given the coordinates, (a:b), (c:d), (e:f), (g:h) of a parallelogram, the coordinates of the meeting point of the diagonals can be found by | {(a+e)/2, (b+f)/2} = {(c+g)/2, (d+h)/2} |

Let W be any point inside a rectangle ABCD, then | WD^2 + WB^2 = WC^2 + WA^2 |

Distance between a point (x,y) and a line represented by the equation ax+by+c=0 is | {ax1+by1+c/Sq(a^2+b^2) |

When a rectangle is inscribed in an isosceles right triangle, then the length of the rectangle is: and ratio of area to triangle area is: | length is twice it's width and ratio of area of a rectangle is triangle is 1:2 |

Length of longest diagonal in a cube is always | XRoot3 where X is the side |

When base area = base perimeter then length of diagonal is always | 4 |

What is the 3D distance formula: | ROOT(L^2 + W^2 + H ^2) |

X^1/2 = | SQ ROOT X |

X^1/3 = | Cube Root X |

X^A/B = 4 different ways which are: | (X^1/B)^A = (X^A)^1/B = (B Root of X)^A = B Root of X^A |

(X-1)^2/X-1 = | (X+1)(X-1)/(X-1) The X-1's cancel out, leaving you X+1 |

3^3 | 27 |

3^4 | 81 |

3^5 | 243 |

3^6 | 729 |

3^7 | 2187 |

3^8 | 6561 |

4^3 | 64 |

4^4 | 256 |

4^5 | 1024 |

Created by:
JustFaded247
on 2009-11-05