A man swims downstream 24km and upstream 16km taking 4 hours each time, what is the speed of the man in still water?
Choices:	A) 8	B) 5	C) 24	D) 12	E) 36

Rationale: "24 - - - 4 ds = 6 ? - - - - 1 16 - - - - 4 us = 4 ? - - - - 1 m = ? m = ( 6 + 4 ) / 2 = 5 answer : b"
Answer: B