Question

B) When heated an iron bar expands by 0.2%. If the increase in length is 1 cm,

Answer 1

Simple algebra.

When we convert this to an equation we get: 0.2% of something is equal to 1 unit.

So here's the equation: $0.02x = 1$

After we transpose $0.02$, the equation become: $x = \frac{1}{0.02}$.

Divide $1$ with $0.02$ and you get $50$.

So the length of the original bar is $50$ cm. :D