Question

2. How many bit strings of length 12 containa) exactly three 1s?b) at most three 1s?c) at least three 1s?d) an equal number of 0s and 1s?

Answer 1

Answer:

The answers are: 220, 299, 4017, and 924.

Explanation:

a) (¹²₃) = 220

b( ¹²₀) + (¹²₁) + (¹²₂) +( ¹²₃) = 1 +12+66+220= 299.

c) 2¹² - 66-12-1 =4017

d) (¹²₆) = 924