Coin riddle

[akahachu]

You walk into a dark room in which one hundred coins are scattered around on the floor. You are told that ten of them have "heads" on top, and that ninety have "tails". Your mission is to separate the coins into two groups such that the amount of coins showing "heads" are equal in each group. You can not see, feel, smell, taste or hear on which side the coins are. Can you perform the mission in a way that it will always work?

[Android Galaxy]

The answer is that you split the coins into a group of ninety and a group of ten. You flip all of the coins in the group of ten. When the lights turn on you'll find that there are an equal number of heads in both groups. It works every time.

[Vertabladehot2m]

He's right, I just tried it in my room...