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. 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 ...
As you note, "percent" means "for every hundred," so there is nothing at all wrong with percent values greater than 100 when discussing proportions, e.g. profits increased by 120%. Like fractions, however, percent values are longer to express than multiples, so for values much greater than 100 you may hear them less frequently:
The type of writing you are doing also plays into your decision. For example, in legally binding documents, like contracts or exhibits to contracts, the spelled out number is the legally binding number. So if a text said that, "you are 99% (one-hundred percent) responsible", the 100% number would be legally binding, not 99%.
If I put "100% correct pronunciation" in the following sentence, is it understandable and correct? "100%" is what I would like to emphasize. If it is not right, how should it be
Joy was founded by 3 friends after one of their sisters was planning her wedding and struggled to find a website that offered personalized attention and detail. The friends built her a custom website to fit her style, and then other wedding guests and friends started asking for one of their own.
If you haven‘t heard of it yet, Joy is a 100% free wedding planning service that helps you create a stunning wedding website, stay organized, and keep your guests in the loop – all in one convenient place.