Temperature variation of resistance

[dasblack]

Homework Statement

A metal wire has a resistance of 8.10 at a temperature of 20°C. If the same wire has a resistance of 11.45 at 90°C, what is the resistance of the wire when its temperature is -20°C?

Homework Equations

R=R(o)[1+alpha(T-To)]
alpha=R-Ro/Ro(T-To)

The Attempt at a Solution

alpha=11.45-8.1 / 11.45(70) = 4.18e-3
R=11.45[1+(4.18e-3)(-40)] = 9.54 ohms
But 9.54 isn't the answer...

 

[LowlyPion]

The Attempt at a Solution

alpha=11.45-8.1 / 11.45(70) = 4.18e-3
R=11.45[1+(4.18e-3)(-40)] = 9.54 ohms
But 9.54 isn't the answer...

Isn't the resistance at 20° = 8.1?

 

[dasblack]

Isn't the resistance at 20° = 8.1?

Hmm.. I did that and got 6.746. It says I am within 10% of the correct value