a boat moves upstream at the rate of 1 km in 40 minutes and down stream 1 km in 12 minutes . then the speed of the current is :
"rate upstream = ( 1 / 40 * 60 ) = 1.5 kmph rate dowm stream = 1 / 12 * 60 = 5 kmph rate of the current = ½ ( 5 - 1.5 ) = 1.75 kmph answer : c"
divide(subtract(multiply(divide(1, 12), const_60), multiply(divide(1, 40), const_60)), const_2)