A problem by crazy singh

Level pending

A steel scale measures the length of a copper rod as $$L$$ cm when both are at 20 degree Celsius, the calibration temperature for the scale. If the coefficient of linear expansion for steel and copper are $$a$$ and $$b$$ respectively, what would be the scale reading ( in cm) when both are at 21 degree Celsius.

1. $$L* \frac{1+b}{1+a}$$

2. $$L* \frac{b}{a}$$

3. $$L* \frac{a}{b}$$

4. $$L$$

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