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

Answer:

3718 ways

Step-by-step 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:

$^{n } C_{r}$

$^{13 } C_{7}$+$^{13 } C_{8}$+$^{13 } C_{9}$

$\frac{n!}{r!(n-r)!}$

$\frac{13!}{7!(13-7)!}$+$\frac{13!}{8!(13-8)!}$+$\frac{13!}{9!(13-9)!}$

1716+1287+715

3718 ways