Jack and Mack both drive 40 km from home to work each day. One day Jack said to mack, "if you drive home at your usual speed, i will average 40 kmph faster than you and arrive home in 20 minutes less time." Find mack's speed.
Jack and Mack both drive 40 km from home to work each day. One day Jack said to mack, "if you drive home at your usual speed, i will average 40 kmph faster than you and arrive home in 20 minutes less time." Find mack's speed.