Yoko read 4 books in 1 h 40 min. She took the same amount of time to read each of the first 3 books. She took 52 min longer to read the fourth book than each of the first 3 books. She finished reading all the books at 22 46. What time did she start reading the fourth book?
Duration that Yoko took to read the first book = 1 u
Duration that Yoko took to read the second book = 1 u
Duration that Yoko took to read the third book = 1 u
Duration that Yoko took to read the fourth book = 1 u + 52 min

Total duration that Yoko took to read the four books 
= 1 u + 1 u + 1 u + 1 u + 52 min
= 4 u + 52 min

4 u + 52 min = 1 h 40 min
4 u = 100 min - 52 min
4 u = 48 min  

1 u = 48 min ÷ 4 = 12 min

Duration that Yoko took to read the fourth book
= 12 min + 52 min
= 64 min
= 1 h 4 min

1 h 4 min before 22 46: 21 42

Time that Yoko started to read the fourth book = 21 42

Answer(s): 21 42