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**A metal wire has a resistance of 8.70 ohms at a temperature of 20°C. If the same wire has a resistance of 11.20 ohms at 90°C, what is the resistance of the wire when its temperature is -20°C?**

**R = Ro[1 + a(T-To)]**

**Basically what I did was found a first by using the 2 given resistances and temperatures:**

11.20 = 8.70[1 + a(90-20)], and I got a = .0041 .

Then I used this a = .0041 to find the R we were looking for (that was the temperature of -20°C):

R = 8.70[1 + .0041(40)], and I get R = 10.12 ohms -- which is wrong.

I'm not sure what I am doing wrong here.

11.20 = 8.70[1 + a(90-20)], and I got a = .0041 .

Then I used this a = .0041 to find the R we were looking for (that was the temperature of -20°C):

R = 8.70[1 + .0041(40)], and I get R = 10.12 ohms -- which is wrong.

I'm not sure what I am doing wrong here.

Any help is appreciated.

Thanks,

Kyle

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