There are 60 birds on a telephone wire and you get bored of bird watching and decide to hunt them.
No bird is colored other than red, yellow, or blue, although some birds may have more than one color.
You start off by shooting 1/2 the birds with red on them, followed by 3/4 of the birds with blue that remain. Then you shoot 1/4 of the birds with yellow that remain, and finally you shoot half of the birds with red that remain.
How many are left?