If a bit string of length 4 is chosen at random, what is the probability of having at least three 1’s?

There are a total of \(2^4 = 16\) outcomes and there are \(\binom{4}{3} + \binom{4}{4} = 5\) ways to have a string with at least three 1’s in it, so the final probability is \(\frac{5}{16}\)