In today's maths course we were given the following problem which was left as an exercise for interested students. How would I go about finding the answer to this?
According to some statistics, people aged 50–60 have a probability $p$ of living at least 15 more years. Similarly, people aged 55–65 have a probability $q$ of living at least 15 more years. What is the probability of people aged 55–60 to still be alive after that period of time?