How do I shade 1/3 of a rectangle

Draw a rectangle, draw three equal lines. Color 1 of those parts!

If you have a coordinate grid, and the rectangle is set up nice, for example it takes up 6 squares, then 1/3 of 6 is 2. You would shade in 2 squares.

But if the rectangle isn't in some grid squares then you can get a ruler, measure the long side. Take 1/3 of the measurement and shade that much.