Question #0c12f

2 Answers
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 #""_13C_4=""_13C_9#