3.1. Discrete Random Variables http://www.ck12.org
P(2 heads)= 204 =20%
#o f favorable choices=12 × 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
( 4 × 3 × 2 × 1 )×( 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 )
#o f favorable choices=479001600
( 24 )×( 40320 )
#o f favorable choices=479001600
967680
#o f favorable choices= 495The number of possible outcomes= 212
The number of possible outcomes= 4096
Now we just divide the numerator by the denominator.
P( 4 heads) =495
4096
P( 4 heads) = 0. 121
P(8 heads) = 19 .7%#o f favorable choices=15 × 14 × 13 × 12 × 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1
( 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1 )×( 7 × 6 × 5 × 4 × 3 × 2 × 1 )
#o f favorable choices=1. 31 × 1012
( 40320 )×( 5040 )
#o f favorable choices=1. 31 × 1012
203212800
#o f favorable choices= 6446The number of possible outcomes= 215
The number of possible outcomes= 32768
Now we just divide the numerator by the denominator.
P( 8 heads) =6446
32768
P( 8 heads) = 0. 197
P(8 heads) = 19 .7%