Is it right to use % symbol in a formula?

Question

I was told when calculating an error term I shouldn't use: $$ Error = 2\% \ast 100kg $$

But that, formally, I should use: $$ Error = \frac{2 \ast 100kg}{100} $$

Which one is right? Or are them both right?

Answer 1

$2$% represents the relative error on the weight, whatever it could be (in other words, it represents more or less the accuracy of the instrument).

Multiplying this $2$% by a given weight gives you the absolute error on the weight. So, if the weight is $100$ kg, the error (or the uncertainty) is $0.02 \times 100 = 2$ kg.

Answer 2

I would say that the second one is correct. Basically 2%=2/100 but you cant write 2%*100, you'd better write (2/100)*100kg or 0,02*100kg