a boat moves upstream at the rate of 1 km in 20 minutes and down stream 1 km in 12 minutes . then the speed of the current is :
rate upstream = ( 1 / 20 * 60 ) = 3 kmph rate dowm stream = 1 / 12 * 60 = 5 kmph rate of the current = ½ ( 5 - 3 ) = 1 kmph answer : a
divide(subtract(multiply(divide(1, 12), const_60), multiply(divide(1, 20), const_60)), const_2)