Jack wakes up late on average 3 days in every 5. If Jack wakes up late, the probability he's late for school = 9/10. If Jack does not wake up late, the probability he's late for school = 3/10. One what percent of days does Jack get to school on time?

Explanation: The probability he wakes up late = 3/5 and the probability he wakes up on time = 2/5. The tree diagram looks like this:

So the probability that Jack gets to school on time = 3/50 + 14/50 = 34%. Jack gets to school on time 34% of the time.