0.2% = 2/100
increase amount over the whole amount
If the increase length is 1cm and you are looking for the whole amount
2/100 = 1/x
Cross multiply
2x = 100
x = 50 cm is the original length of the bar
Checking you answer,
0.2% of 50 is 0.02 × 50 which is 1 so the answer is correct.
The original length of the bar is 50 cm.