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When someone uses the phrase "percent increase" what does that mean?

For example, if something took $4$ seconds before and now it takes $1$ second, would that be a $400$% increase?

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  • $\begingroup$ I'm new to this stack exchange; care to clarify the down vote on the question? $\endgroup$
    – hbhakhra
    Feb 21, 2014 at 0:37
  • $\begingroup$ I can't see a reason to down vote your question. I wouldn't worry about it. $\endgroup$
    – 2'5 9'2
    Feb 21, 2014 at 0:39
  • $\begingroup$ If it goes from 4 to 1 it would be a $75\%$ decrease in time, or a $300\%$ increase in speed. Usually when people talk of percent increase or decrease they are up to no good and often they are incorrect mathematically. $\endgroup$ Feb 21, 2014 at 0:46

1 Answer 1

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$A$ is a $B\%$ increase over $C$ iff $100\times(A/C-1)=B$ where the minus one is because of the "increase" part (and the 100 is because of the "percent" part).

That is, 4 is a 300% increase over 1. A 0% increase over 1 would just be 1, while a 100% increase would be 2.

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