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GRE Math
Concepts & Tricks from Kaplan's 2011-2012 Reference Section
6
Mathematics
9th Grade
11/30/2011

Additional Mathematics Flashcards

 


 

Cards

Term

How to find the

SUM OF CONSECUTIVE NUMBERS

 

(Ex: What is the sum of the integers from 10 through 50, inclusive?)

Definition

(Average) * (# of terms) = (Sum)


Ex:

Average = (10+50)/2 = 30

# of terms = 50 - 10 + 1 = 41

Sum = 30 * 41 = 1,230

Term

How to solve a

COMPOUND INTEREST PROBLEM

 

(Ex: If $10,000 is invested at 8% annual interest, compounded semiannually, what is the balance after 1 year?)

Definition

(Principal) * (1 + r/C)T*C = (Final Balance)

where C is # of time compounded annually

and T is time.

 

($10,000) * [1 + (.08)/(2)](1)*(2) = $10,816

Term

How to solve a

COMBINED WORK PROBLEM

 

(What is the limitation of this formula and

how can I solve it otherwise?)

Definition

The inverse of the time it would take everyone working together equals the sum of the inverses of the times it would take each working individually.


If the problem refers to different tasks (painting 1 house versus painting 4 houses, etc.) you should just compute man-hours or union-years, etc.

Term

How to solve a

GROUP PROBLEM INVOLVING BOTH/NEITHER

or a

GROUP PROB INVOLVING EITHER/OR CATEGORIES

Definition

Both/neither:

VENN DIAGRAM or

Group1 + Group2 + Neither - Both = Total

 

Either/or:

2x2-cross grid

Term

How to solve a PERMUTATION problem

 

(What is the formula?

&

Does order matter?)

Definition

nPk = n! / (n-k)!

where n = (# in the larger group) &

k = (# you're arranging)

 

Order matters (how many possible arrangements are there?)

Term

How to solve a COMBINATION problem

 

(Does order matter?

&

What's the formula?)

Definition

 

nCk = n! / k!(n-k)!

where n = (# in the larger group) &

k = (# you're choosing)

 

Order DOESN'T matter (How many different ways to choose k?)

 

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