Hi Fred.

The word "increase" might make you wonder if you should divide $2500 by $500 rather than $3000 by $500, but really it is universally understood that the word is just part of the whole term "n-fold increase" and has no practical effect on the meaning.

When we say "the stock went up two-fold" or "it had a two-fold increase" or "it doubled", we are saying the same thing in all cases. A two-fold increase means the final amount is twice the original amount. So going from $500 to $3000 is a six-fold increase, because $3000/$500 is 6.

Don't let the word "increase" confuse you, just chalk it up to another one of the many peculiarities of the english language.

Stephen La Rocque.