Is there a rule about when the preposition "by" should be used (when talking about percents - falling, increasing, rising etc.)?
I've read the sentences below in different articles today: 1. ... profits rose 11 percent to 2.7bn dollars.
2. Revenues increased 11.6 percent from 229bn dollars to 256bn dollars.
3. They said pre-tax profit soared 18.5 percent at their stores.
4. ... output has fallen by up to 20% in one year.
My question is: when do you use "by" to say how much "by how many percent" something grew/fell etc.?
Do you use "by" just with the verb "to fall"?