Menopause brings a lot of change, and it’s normal to feel uncertain about what’s happening in your body. Two of the most important hormone players in this transition are estrogen and progesterone. The flow rate increases 100-fold (one hundred-fold) Would be a more idiomatic way of saying this, however, the questioner asks specifically about the original phrasing.

Understanding the Context

The above Ngram search would suggest that a one hundred has always been less frequently used in written language and as such should probably be avoided. Your other suggestion of by one hundred times is definitely better than a ... If soap A kills 100% and soap B kills 99.99% of bacteria, the remaining amount of bacteria after applying A (0%) is infinitely smaller than the remaining amount of bacteria after applying B (0.01%). Therefore A is much, much better.

Key Insights

You can see from these examples that 0.01% gap behaves differently across the percentage scale. Yes, the correct usage is that 100% increase is the same as a two-fold increase. The reason is that when using percentages we are referring to the difference between the final amount and the initial amount as a fraction (or percent) of the original amount. Why is "a 100% increase" the same amount as "a two-fold increase"? People often say that percentages greater than 100 make no sense because you can't have more than all of something.

Final Thoughts

This is simply silly and mathematically ignorant. A percentage is just a ratio between two numbers. There are many situations where it is perfectly reasonable for the numerator of a fraction to be greater than the denominator. relating to 100 years : marking or beginning a century, with the example "the centurial years 1600 and 1700". But there is a word that is widely used to indicate the range of years or centuries covered by an article or book: history. And the usage always seems to involve a number between 100 and 200: "a buck fifty" and so forth (the term seems to be wedded to the indefinite article: "a buck something ").