let's imagine that a student got 0 marks in a exam. And in the next one he got 5 marks. to calculate the percentage of the new mark to the last mark, we usually use (new-last)/last*100%. but the denominator is 0. So the expression should be (5-0)/0*100%, right? But 0 as denominator will result in error in calculator. So how to calculate?
The percentage of a number to zero
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0@JohannesKloos Could you promote your comment to an answer so as to remove this question from the Unanswered queue? You could also incorporate the alternative method $100(1-\exp(-\frac{\text{new mark}}{\text{old mark}}))$ that Angela proposes. – 2013-06-06
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No, this is not possible - there is no way to give a useful percentage value here. This is because there is no number $p$ such that $p\cdot0=5$, so there is also no percentage.
Alternatively, as Angela proposes, instead of measuring the percentage change in marks, an improvement rating out of $100$ could be given by $100(1−\exp(-\frac{\text{new mark}}{\text{old mark}}))$. Then as $\text{old mark}\to0$, the rating goes to $1$, and the ratings of students who score low and improve slightly do not dwarf those of students who score fairly high and subsequently improve a lot.