What Temperature Makes Copper and Iron Wires Equally Resistant?

[electricblue7]

Homework Statement

A copper wire has a resistance of 0.501 ohms at 20.0 degrees C, and an iron wire has a resistance of 0.466 ohms at the same temperature. At what temperature are their resistances equal?

Homework Equations

R = Ro {1 - coefficient of expansion *(T - To)}

The Attempt at a Solution

R(iron) = Ro {1 - coefficient of expansion *(T - To)}

R(copper) = Ro {1 - coefficient of expansion *(T - To)}

I set R(iron) = R (copper) and solved for the Temperature final, but the answer was wrong. Can you help me? Thanks!

 

[Mapes]

The increase in resistance due to a length increase via thermal expansion is probably negligible compared to the increase in resistance due to a positive temperature coefficient of resistivity.