# Question 0c12f

Sep 22, 2016

"_13C_4 = 715

#### Explanation:

this seems like a combination problem where we select "_13C_4 = 715. this means that out of the 13 times there are 715 where times where we can group 4 items differently in this case representing the heads.

Sep 22, 2016

""_13C_4=(13!)/(4!*9!)=715

#### Explanation:

You have a sequence of $13$ outcomes;
Exactly $4$ of these outcomes must be Heads;
that is, we need to choose $4$ locations within $13$ where Heads are to occur.

""_13C_4=(13!)/(4! * 9!)=(13xx12xx11xx10)/(4xx3xx2xx1)=715#

Note: we could have just as well thought of this as choosing $9$ locations in the sequence for the Tails since ${\text{_13C_4=}}_{13} {C}_{9}$