Today Puzzle #537
Puzzle No. 537 鈥� Friday 2 August
A planet has three moons. They are currently all aligned and the closest moon will take one year to orbit the planet. The middle moon is 3 times further from the closest moon than the closest moon is to the planet. The farthest moon is 5 times as far away from the middle moon as the closest moon is from the planet. When will the moons next be aligned over the same spot on the planet? [You may assume they all take circular orbits]
Today’s #PuzzleForToday has been set by David Hargreaves, Visiting Lecturer, Faculty of Actuarial Science and Insurance, Cass Business School
Click here for the answer
216 years
Explanation
Moons are distances 1, 4 and 9 from the planet
Length of orbit is therefore in a ratio 1:8:27 (By Kepler’s law)
216 is then just the lowest common multiple of 1, 8 and 27
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