A Cool Puzzle

Here is a cool puzzle. Dont remember where I came across this one. All credit to its original author. It goes something like this.
5 Mathematicians and one wise man caught in enemy territory.They have half an hour to device a strategy to solve a problem failing which they all die. The problem...
The 5 mathematicians are made to stand in a circle. A hat is put on each one's head that carries a number between 1 and 9, including the extremes, on it. They cannot communicate in any way what so ever else they all get hanged. The wise man has two coins one Blue and one Red. After the hats are placed on each mathematician's head, the wise man can walk in and handover one coin out of the two to one person of his choice and walk away. After that, the enemy picks one (any) mathematician in the circle at random and asks the number on his head. If he is correct all live else all die.
What is the strategy that saves their lives?

• A number can be repeated
• One mathematician in the circle can see all the other 4 numbers.