Two students who live on planet X. They want to estimate the circumference. The two students synchronize their watches before one student leaves on vacation 600 miles due west to their home. They notice a 3 degree difference in altitude of the sun at local noon. What is the circumference of the planet?

72000 miles

Explanation:

If the distance between the students is 600 miles, and this implies in a 3 degree difference in the sun position, that means this 600 miles is related to 3 degrees of the circunference of the planet.

So, to find the whole circunference of the planet, that is, 360 degrees, we just need to use a rule of three:

3 degrees - > 600 miles

360 degrees - > x miles

3x = 600 * 360

x = 600 * 360 / 3 = 72000 miles