a train is moving at 4 / 5 of its usual speed . the train is 30 minutes too late . what is the usual time ( in hours ) for the train to complete the journey ?
"new time = d / ( 4 v / 5 ) = 5 / 4 * usual time 30 minutes represents 1 / 4 of the usual time . the usual time is 2 hours . the answer is c ."
divide(multiply(multiply(30, divide(4, 5)), inverse(subtract(const_1, divide(4, 5)))), const_60)