I tried searching online and I found several examples of doing such problems, but I'm still not sure if I'm doing them correctly and would greatly appreciate some help!
How many bit strings of length 20 have:
a.) exactly four 1's
b.) at most four 1's
C.) at least four 1's
Like I said I've found similar problems but I get different solutions when applying them with my specifics. I think I may have gotten a and b, but not sure about c. Did I do them correctly? Thanks!