Question

One week a librarian kept track of whether returned books were returned on time or not, and whether they had fewer than 200 pages or they had 200 pages or more. The results are shown in the table.

What is the probability that a randomly selected book returned that week was returned on time, given that it had 200 pages or more?




Returned on time

fewer than 200 pages—— 78

200 pages or more ——116



Returned late

Fewer than 200 pages ——-15
200 pages or more ——31

Answer 1

In total, there were 147 books returned that week that had more than 200 pages. If 116 of those were returned on time, then 31 were returned late. This is about 79 percent of the 147 total. So, there is about a 79% chance that a randomly selected book with 200 pages or more was returned on time, or about 79/100.