2 How many bit strings of length 12 contain at most nine 1s

2. How many bit strings of length 12 contain at most nine 1\'s and at least nine 0\'s? Fully evaluate the result.

Solution

From given data:

Length of string:12

and we need to select 1\'s :at most 9

        and need to select 0\'s: at least 9

in different ways we can bit string of length 12

first take: 0\'s 9 then 1\'s 3

                  0\'s 10 then 1,s 2

                  0\'s   11 then 1\'s 1

                  0\'s     12 then 1\'s 0

From the above combination of way\'s we can select and arrange string length is 12.

ans: 4