
Chapter 6
212
Example 6.1
Consider a fair coin tossing experiment. What is the probability of getting two heads in three trials?
Solution: As discussed above,
The probability of x success in n trials = P(x) =
n
nx x
pq
xnx
!
()!( )!−
−
Probability of getting two head in three trials =
3
322
05 05
2
!
!!()()
(.)(.)
−
−
=
××
××
321
2111
05 05
2
()()
(.)(
=
6
02505(. )(
= 0.375
So, the probability of getting two heads in three trials is 0.375.
6.4.2 Using MS Excel for Binomial Probability Computation in Example 6.1
In Example 6.1, computation was very simple and could be done manually very easily. In a few
cases, like computing the probability of getting 140 ...