brainbuster no. 26 - a load of balls

This competition closes on Sunday 31 August 2008.

the brainbuster

In a box there are 13 white balls and 15 black balls. There are also 28 black balls outside the box.

You remove two balls from the box. If they are different colours, you put the white one back in the box. If they are the same colour, you put a black ball into the box.

You continue doing this until only one ball is left in the box.

What colour is it? Explain why.

thinkingpeoplefirst