Question

How many ways can a person toss a coin 13 times so that the number of tails is between 7 and 9 inclusive

Answer 1

3718 ways

Explanation:

How many ways can a person toss a coin 13 times so that the number of tails is between 7 and 9 inclusive

Probability is the likelihood for an event to occur or not

The formula for a combination is:

n choose r = n! / (r! x (n-r)!)

n=13

r=7 to 9

We are going to add up the cases for 7 through 9:

`^(n ) C_(r)`

`^(13 ) C_(7)`+
`^(13 ) C_(8)`+
`^(13 ) C_(9)`

`(n!)/(r!(n-r)!)`

`(13!)/(7!(13-7)!)`+
`(13!)/(8!(13-8)!)`+
`(13!)/(9!(13-9)!)`

1716+1287+715

3718 ways