You can't use a preposition before adjectives (unless they modify nouns) or adverbs, but a prepositional phrase can be adjectival or adverbial.
Student or Learner
Can we use prepositions before adverbs or adjectives?
Is it correct to say: "In 2008, stock prices went down thrice." or "In 2008, stock prices went down by three times."
Please explain as I am trying to figure out it for a long time on internet but did not get the good result.
Thanks in advance.
***** NOT A TEACHER *****
I just thought that you might be interested in something that I found in one of my favorite books.
"In a few idiomatic expressions, an adverb or adjective is used as the object, and thus becomes a noun-equivalent."
1. I did not know her until now.
2. They will go from there,
3. We worked in vain.
4. They looked on high for help.
Source: Walter Kay Smart, English Review Grammar (1940).
Your two sentences don't have the same meaning, and possibly don't mean what you want them to mean. Thrice means three times, not 'by three times'.
Do you mean that in 2008 stock prices went down on three occasions (which seems highly unlikely), or that they dropped to a third of their previous level by the end of 2008?
Parser, things must have changed in the past 75 years.
In some dictionaries, "now" is classified as a noun.
In some dictionaries, "there" is classified as a pronoun.
"In vain" in considered an idiom by many.
In some dictionaries, "high" is classified as a noun.
These uses are not unusual.
They dropped to a third of their previous level by the end of 2008.
How can I make a proper statement regarding it in a general way?
Which one of my above written statements is true?
None. They didn't drop three times their initial level. They dropped two thirds.
Stock prices can't drop by more than 1 time their initial value, or they'd become negative, which doesn't normally occur, to my knowledge. They can have dropped by three times their current level, for example if they dropped from $4 to $1. That's a drop of three quarters of their initial level.
If I have to say from current level, then what.
If they are going to drop from their current level, you'd have to wait and see what happens. But if you know this, sell!
If you want to tell us how much they are, X, and how much they will be, Y, we can tell you.