Once upon a time, there was a garden somewhere in the world. In that garden, there were some birds on the ground and some birds on a tree.
The birds on the tree say to the birds on the ground that if one of you came to our tree, then our population will be double of yours.
Then the birds on the ground tell the birds on the tree that if one of you came to the ground, then our population will be equal to that of yours.
How many birds were on the ground and how many birds were on the tree?
