Question

Jupiter takes 12 earth years to orbit the sun, and Uranus takes 84 earth hears to complete one revolution around the sun. If both the planets are aligned in a straight line tonight, how many years will it be until they are aligned in the same position again? (Orbital periods are rounded)

Answer 1

Answer: 84 years

Reason:

84 is a multiple of 12 (because 84/12 = 7), which means it takes 84 years for the two planets to align again.

In other words, the LCM of 84 and 12 is 84. The LCM is when things line up again.