Chapter 3

Question 1

probaability of an event =

Answer 1

Total number of possible outcomes

Question 2

If one event can happen in p different ways and another event can happen in q different
ways then

Answer 2

the 2 successive events can happen in pq different ways

Question 3

Pigeonhole Principle

If n + 1 or more pigeons are placed into n pigeonholes, then

Answer 3

at least one pigeonhole must
contain 2 or more pigeons

Question 4

Further Pigeonhole Principle

If n pigeons are placed into k pigeonholes where n>k, then

Answer 4

at least one pigeonhole must contain at least n/k pigeons

Question 5

Factorial Notation

n!

Answer 5

n(n-1)(n-2)(n-3)….3 * 2 * 1

Question 6

0!

Answer 6

1

Question 7

ⁿPᵣ

Answer 7

n!/
(n-r)!