LCM question using Astronomy

Who says teaching Arithmetic is boring? Perhaps having a context will help students get more interested in finding the lowest common multiple (LCM) of numbers and highest common factor of numbers (HCF), and perhaps understand the importance of these 2 concepts. One area of science where LCM can be applied is astronomy as illustrated by the following:

Suppose Jupiter takes 12 years to make on revolution around the sun, and Saturn takes 30 years. If these 2 planets were to line up in the Earth sky, how long would it take for them to line up in the Earth sky again?

Adapted from Teaching Secondary Mathematics through Applications (2nd Ed.), Herbert Fremont. A highly recommended read for any one who would like to find interesting applications of high school mathematics.