A boy presses a side of a blue pencil to a side of a yellow pencil, holding both pencils vertically. One inch of the pressed side of the blue pencil, measuring from its lower end, is smeared with paint. The yellow pencil is held steady while the boy sl
At the start, 1 inch of the yellow pencil gets smeared with wet paint. As the blue pencil is moved downwards, a second inch of the blue pencils smears a second inch of the yellow pencil.