A boat moves upstream at the rate of 1 km in 20 minutes and down stream 1 km in 15 minutes. Then the speed of the current is : Choose the correct choice from the following answers
A) 1 kmph	B) 0.5 kmph	C) 3 kmph	D) 2.5 kmph	E) 3.5 kmph

Rationale: "rate upstream = ( 1 / 20 * 60 ) = 3 kmph rate down stream = 1 / 15 * 60 = 4 kmph rate of the current = ½ ( 4 - 3 ) = 0.5 kmph answer : b"
Answer: B