## Nov 10, 2009

### 25 cards in a dark room

A deck of 25 cards, 14 of which are facing up & 11 are facing down, is lying on a table in a dark room. You are asked to go in that room and split the deck into two such that total number of cards facing up in each deck are equal. How do you do that?

#### 4 comments:

1. Turn the light on.

2. Well surely....But can u do it without turning it on????

3. If you split the pack, turn each deck on it's end and lean them against each other in an upright position there will be 0 cards facing upwards in each.

4. haha clever!! :P

Alternatively, split the deck into 14 and 11. Turn the entire 14-cards deck around and you'll have the problem solved.

You can check mathematically by assuming that there are 'x' cards facing down in 11-cards deck. Thus, 11-x cards are facing up in 11-cards deck. Now, in 14 cards-deck there will be 11-x cards facing down (since total number of cards facing down is 11). Turn the 14 cards deck around. Thus, we'll have 11-x cards facing up in both the decks. Problem solved!