The Psychology of Arithmetic

by Edward L. Thorndike

Fig. 52.—What are these drawings intended to show? What simple change would make them show the facts much more clearly?

Fig. 53.—Arranged in convenient "eye-fulls."

Fig. 54.—Clear, simple, and easy of comparison.

Tell which bar has—
1. About 5 percent of its length black.
2. About 10 percent of its length black.
3. About 25 percent of its length black.
4. About 75 percent of its length black.
5. About 90 percent of its length black.
6. About 95 percent of its length black.