expected value

The probability of an event happening in 2017, 2018,2019, 2020 and 2021 is 0.4 , 0.3, 0.2, 0.5 and 0.1 respectively. The probabilities given are conditional. This implies that the probability that the event will occur in 2020 given that it does not occur in 2107,2018 and 2019 is 0.5.

The event can happen only once in the 5 years.

What is the expected time of the event in years.