Posted by **dan** on Sunday, July 29, 2012 at 5:22pm.

Planets A, B and C orbit a certain star once every 3, 7, and 18 months respectively. If the three planets are now in the same straight line, what is the smallest number of months that must pass before they line up again?

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**Reiny**, Sunday, July 29, 2012 at 5:25pm
hint: what is the LCM of 3,7, and 18 ?

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**dan**, Sunday, July 29, 2012 at 5:29pm
72

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**Ms. Sue**, Sunday, July 29, 2012 at 5:32pm
72/7 = ?

Try again.

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**dan**, Sunday, July 29, 2012 at 5:34pm
Oops I was thinking of 8 times 9

It's 126

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**Ms. Sue**, Sunday, July 29, 2012 at 5:40pm
Right.

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