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Yes, resistors in series add. Or, equal resistors in parallel divide by 2 - you may have 2 100k resistors which in parallel would make a 50k
From what I can see, it looks like this is what the NJ-HR group did. 2 100k resistors in parallel (50k) in lieu of a 51k.
That is correct. Radio Shack didn't have a 51K, so I used two 100Ks in parallel
Bob D