Betty read 3 books in 3 h. She took the same amount of time to read each of the first 2 books. She took 48 min longer to read the third book than each of the first 2 books. She finished reading all the books at 15 31. What time did she start reading the third book?
Duration that Betty took to read the first book = 1 u
Duration that Betty took to read the second book = 1 u
Duration that Betty took to read the third book = 1 u + 48 min

Total duration that Betty took to read the three books 
= 1 u + 1 u + 1 u + 48 min
= 3 u + 48 min

3 u + 48 min = 3 h
3 u = 180 min - 48 min
3 u = 132 min  

1 u = 132 min ÷ 3 = 44 min

Duration that Betty took to read the third book
= 44 min + 48 min
= 92 min
= 1 h 32 min

1 h 32 min before 15 31: 13 59

Time that Betty started to read the third book = 13 59

Answer(s): 13 59