Teenagers versus adults... (Updated)

In the next week or so, I will be posting three problems for anyone under the age of sixteen to have a go at.  The prize is epic - two whole movie tickets.

The reason is, is that many folks are busy working away on number problems that have little extrinsic reward.  To those of you actively learning mathematics - well done.  It will pay off, plus it's just good fun.

This weeks challenge

There is a problem below that will test you.  What I would like to do is have a little competition between teenagers and adults.  I am wondering if teenagers can solve this quicker than their parents!  I suspect they might.

Game on people - post your answer in the comments.  Good luck.

Zombie apocalypse

The apocalypse happened.  It was bad, and only a few survived.  However, you have become the leader of a rag-tag group of survivors.  You are doing well, but MUST get out of the city.

As you walk along you come across a truck that will be able to carry almost everyone.  You load everyone on board except you and three others.

As the truck leaves you tell the driver to travel at fifty kilometers an hour only.  They will be on a highway so will be able to keep this speed steady.  You do this so that you will know where they are at all times.  All phones and electricity are out so you don't want to get lost.  You want to be able to catch up to them.

Because the four of you had to find a car, you leave one hour later.  If you travel at 80 kilometers an hour, and they are traveling at 50 kilometers an hour, how long will it take to catch the rest of your group?

Good luck.

Update:  Seems the good people of Hastings are the quickest!

Update two:  Maths is really only maths if you have no method that can be used to solve the problem.  Instead you have to draw on your wits, cunning and resources.  Some people draw pictures of cars, some work out where each vehicle will be at certain time zones, some work backwards, some draw graphs and so on.  It's the HUNT, that makes maths cool, not the answers.  Enjoy the process... that's where the fun is.