I am having some trouble with statistics and there isn't anything in my book to help me.
A Binary String is a sequence of digits either 0 or 1.
a.) How many binary strings of length 9 are there? (The first digit may be zero).
b.) How many binary strings of length 9 contain the digit 1 exactly 3 times?
c.) How many binary strings of length 9 alternate 0’s and 1’s?
d.) How many binary strings of length 9 have an even number of 1’s?