Question 836260
The planet Jupiter goes around the sun in 12 years (approximately) and the planet Saturn in 29 years. In how many years will the planet Jupiter gain one complete circuit on the planet Saturn? 
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Using 12 and 29 years, and starting at a syzygy at angle = zero:
J's angle = (360/12)*t = 30t, t in years, angles in degrees
S's angle = (360/29)*t
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Find when the angles are equal modulo 360, which is 360< angle < 720
30t  = 360t/29 + 360
t = 12t/29 + 12
29t = 12t + 348
17t = 348
t =~ 20.47 years
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It's the product/difference of the periods