Rainer's Mensa Pages

John was on a business trip and arrived at the train station of his home town. He went to a public phone and called his wife to tell her that he arrived and will walk to their home which he did after hanging up the phone. His wife noticed that it is a good opportunity for a little walk with their dog Spike and told John that she will come to meet him on the way. Since it was a warm evening she did not need a coat and could just call Spike and walk out of the door.

The distance between their home and the train station is 5 km. Jane had a busy day, but felt still fit and so she walked with a velocity of 4 km/h. John had a bad meal in the train, therefore decided to take it easy and walked with a velocity of 2 km/h. Spike, the dog, left the home the moment Jane went out of the front door and ran towards the station. When Spike met John, he wagged his tail and decided to run back to Jane. When he arrived at Janes location, he wagged his tail again and ran back to John and so he kept running back and forth between them until John and Jane met each other.

Assuming Spike runs with a velocity of 9 km/h, which distance did he cover until John and Jane met?