We already have the diameter of the coin, the distance between Carol and Hamza (wich is the distance between “eye” and coin) and the distance from Earth to the Moon (wich is the distance from “eye” to the Moon).

We'd like to work out the Moon's diameter this being twice the radius.

If you get bogged down, here you have some directions as to how to find the solution:

• Draw freehand a geometric picture of the problem situation on your piece of paper. It should be similar to the dynamic applet.
• Watch the following dynamic applet… The orange lines are parallel lines (and purple ones as well)

• So, we have to use our mathematical knowledge to go on…, what about Thales' theorem? Do you think is it appropiate to use it? Why?
• Watch the following dynamic applet and then, look at your drawing. Do you find any similarity?

• Put Thales' theorem into practice.
• Work out the value of Moon's diameter.
• Is your solution possible? (for instance, 500m would be impossible!)