The GMAT Forum

Probability = Number of favorable outcomes / Total number of outcomes

If an event occurs in A ways and fails in B ways then
Probability of occurring an event
P(A) = A / A + B
P(B) failing of event = B / A + B or 1 - P(A)

Permutation and Combination:

Permutation nPr = n! / (n-r)!
Combination nCr = n! / (r!) (n-r)!
If one operation can be performed in M ways and the second operation can be performed in N then the number of ways of performing the two operations is
M * N

If there are variables in the question substitute them with numbers and try to solve.

At a certain printing plant each of m machines print 6 newspapers in every s seconds. If all machines work together and independently without interruption
How many minutes will it take to print 1800 newspapers?
a) 180 s / m
b) 50 s / m
c) 50ms
d) ms / 50
e) 300 m / s

Typically, in these problems, we start by letting x be a person's current age and then the person's age a years ago will be x - a and the person's age a years in future will be x + a. An example will illustrate.

In solving coin problems it is best to change the value of all monies involved to cents before writing an equation.

1 Nickel = 5 cents
1 dime = 10 cents
1 quarter = 25 cents
1 half = 50 cents
1 dollar = 100 cents

Laura has 20 coins consisting of quarters and dimes. If she has a total of $3.05, how many dimes does she have?
A. 3
B. 7
C. 10
D. 13
E. 16

Simple Interest:

SI = PRT / 100

A = P + SI

A student invests 4000, part at 6% and part at 7%. The income from these investments in 1 year is 250. Find the amount invested at 7%.

250 = I1 + I2

Let x be the amount invested for 7%.

250 = (4000-x)*6 / 100 + x*7/100

x = 1000.

A total of 1200$ is deposited in 2 semi annual accounts for one year. Part at 5% and remainder at 10%. If 72$ was earned as interest How much was deposited at 5%?