Cross Multiplication
Cross Multiplication for Proportionalities
An electrician needs to be able to use proportionality to solve a problem
about conductor resistance at length. Here's how it works. If a certain
conductor has a resistance of 18 ohms per 1000 feet, what will the resistance be
for, say, 500 feet? 9 ohms, you come up with. Right. But if the length is not an
exact half, or some other common fraction, how is the solution determined?
Cross multiplication can do it.
A over B equals C over D
Or, A times D divided by B equals C. Sound difficult? Let me explain.
If a conductor is (A)18 ohms per (B) 1000 feet, then what is the
resistance (C) at (d)500 feet?
So it is A times D divided by B equals C.
Or 18 times 500 divided by 1000 equals 9.
Works every time.
Find practice problems HERE.
Find audio support HERE.
