A swimmer swims downstream 55 km and upstream 10 km taking 5 hours each time; what is the speed of the current?  Choose the correct answer.
A) 4.6	B) 4.5	C) 4.4	D) 4.3	E) 4.2

Rationale: 55 - - - 5 ds = 11 ? - - - - 1 10 - - - - 5 us = 2 ? - - - - 1 s = ? s = ( 11 - 2 ) / 2 = 4.5 answer : b
Answer: B