Moe and May went to the beach the other day.
While May was setting out food for the picnic, Moe collected a bagful of pretty stones.
When he returned, he spread them out on the cloth for Mae to see.
Take as many of them as you like, he said, and put them in your bag.
While you finish preparing the food I'll fill my bag with more stones.
When they returned home, they counted their stones.
What is the probability they had an even number of stones between them? [edit]