a car was driving at 50 km / h for 30 minutes , and then at 90 km / h for another 40 minutes . what was its average speed ?
"driving at 50 km / h for 30 minutes , distance covered = 50 * 1 / 2 = 25 km driving at 90 km / h for 40 minutes , distance covered = 90 * 2 / 3 = 60 km average speed = total distance / total time = 85 / 5 / 6 = 102 km / h answer : a"
divide(add(multiply(divide(30, add(30, 40)), 50), multiply(divide(40, add(30, 40)), 90)), divide(add(30, 40), const_60))