Coin Distances Print Play

Coin Distances after Martin Gardner Home / Puzzle Playground / Illusions /

Fig. 1

Fig. 2

Place three identical coins side by side as shown in Figure 1. Now, can you slide the middle coin to the right along the horizontal line until distance AB equals distance CD? As you slide the middle coin to the right distance CD is unfolded as shown in Figure 2. The object is only to guess the place where CD is unfolded enough to be equal AB.

Last Updated: June 11, 2005 Copyright © 2005 ThinkFun Inc. All Rights Reserved. Permission is granted for personal use only. This puzzle may not be duplicated for personal profit.

Page 1 of 2

Coin Distances Explanation Home / Puzzle Playground / Illusions /

The illusion is perhaps related to the Müller-Lyer illusion, when two lines of equal length appear different because of arrow lines that point inward at the ends of one line and outward at the ends of the other. In our illusion the coins' rims play the role of the arrows. With distance AB the rims of the respective coins lay within the length of AB. While for distance CD the rims are outside its length. As a result this makes an illusion that distance AB seems to be somewhat shorter than distance CD, though they are in fact equal.

Last Updated: June 11, 2005 Copyright © 2005 ThinkFun Inc. All Rights Reserved. Permission is granted for personal use only. This puzzle may not be duplicated for personal profit.

Page 2 of 2