# What is the missing element in this series: 2, 5, 8, 11, [missing item goes here

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SidKempposted 5 years ago

What is the missing element in this series: 2, 5, 8, 11, [missing item goes here], 15, 19, 22, 30.

Note: This problem may not be mathematical. For a bonus, say where the series came from.

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calculus-geometryposted 5 years ago

I thought about this one for quite a while, but you have me stumped.  Assuming that the sequence is finite and ends at 30, my best guess is that these numbers correspond to calendar dates, though what dates they are I can't figure out.  Looking forward to seeing the solution.

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SidKempposted 5 years agoin reply to this

2 hints: Don't assume the missing element is a number. Take a look at Philadelphia.

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brettmwposted 5 years ago

A little obscure of a question. Don't know how anyone that isn't a regular user of Philadelphia public transportation would have known this, but it's stops by the Market-Frankford subway line. According to wikipedia the next stop is 13th street. If you were looking for City Hall as an answer that comes after the stop at 15th street. Or wikipedia could have it wrong.

http://en.wikipedia.org/wiki/Market%E2% … Line#Route

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SidKempposted 5 years agoin reply to this

You've got the right source. Find an older name for 13th street stop, which is not a number, and you'll have the answer, the stop as it was named in the 1970s. It's the street between 13th & City Hall. Warning, it's is on Google maps, but not nam

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brettmwposted 5 years agoin reply to this

Well then that would be Juniper Street.

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SidKempposted 5 years agoin reply to this

You got it! This was a puzzle in my brother's HS math class. The argument was over whether this list constituted a pattern. I argued then and now:  this is a series, but not a pattern: 2, 5, 8. 11, Juniper, 15, 19, 22, 30 (after that, not a subway!)

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brettmwposted 5 years agoin reply to this

I agree. This is definitely not a pattern. A series describes this list more accurately.

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tussinposted 5 years agoin reply to this

That's a good one, Sid.  You didn't have to give away that you saw the problem somewhere else, you could have pretended that you came up with it.

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