For resistors in series:

R1 + R2 + R3 + ... = R(TOTAL)

For the special case of only two resistors in parallel:

R1 X R2
------- = R(TOTAL)
R1 + R2

general case:

1
----------------- = R(TOTAL)
1 1 1
--- + --- + --- + ...
R1 R2 R3


For extra credit, prove that

R1 X R2
------- = R(TOTAL)
R1 + R2

is in fact the same as

1
----------- = R(TOTAL)
1 1
--- + ---
R1 R2


Unless you are a crackerjack math wiz, these equations look totally
different. Another point of confusion.


And the stuff cavemen knew would be stuff a city boy like myself doesn't
have a clue about. How to hunt animals with nothing better than crude
spears and rocks, knowing what plants are safe to eat and what's
poisonous, etc.... Different environments, they didn't need to know
about car insurance.