To get the probability of a single random event, this formula must be followed
Probability = event/s / number of outcomes
In this problem, the number of outcomes is 80% 40% and 25%. The event is that a person owns a tablet computer that owns also a smartphone.
.8 +.4+.25 = 1.45 x 100 = 145%
Probability = .25 / 1.45= 0.1724 x 100 = 17.24%
Therefore, the probability that a person owns a tablet computer and smartphone is 17.24%.