When dropped on a hard surface a thumbtack lands with its sharp point touching the surface with probability 2l3; it lands with its sharp point directed up into the air with probability 113. The tack is dropped and its landing position observed 15 times. 3. Find the probability that it lands with its point in the air at least 7 times. b. If the experiment of dropping the tack 15 times is done repeatedly, what is the average number of times it lands with its point in the air