Which one is correct and what is the difference between them?
1 The amount of sales was standing at $10000 in 1990.
2 The amount of sales stood at $10000 in 1990.
For example, consider this question in this context:
Suppose that the data that we have is that the amount of sales in 1989 was $5000, in 1990 was $10000, and in 1991 was $15000. Now suppose that we want to write a formal report about this data. Are both example sentences in my question legitimate and correct in this context?
In those sentences there is no significant difference, just a matter of style. Both are grammatically valid, although I think (2) is more common. However, in other uses, there can be a difference.
(3) He was standing on the corner.
(4) He stood on the corner.
In (3) at the moment of interest "he" was in the process of standing on the corner.
In (4) he stood on the corner at some unspecified time in the past (or with the proper context in the present). And of course there are other senses of "standing" and "stood" that are not even close to interchangeable, such as:
(5) One must have standing to bring a lawsuit.
(6) She stood to gain a lot if the deal went through.
Progressive Past Tense
The progressive past tense (also known as the Past Continuous Tense):
The past continuous tense, also known as the past progressive tense, refers to a continuing action or state that was happening at some point in the past. The past continuous tense is formed by combining the past tense of to be (i.e., was/were) with the verb’s present participle (-ing word).
"Was standing" identifies an action that took place in the past that, from the perspective of the past, was still happening. "He was standing there when I left," meaning that the person continued to stand in the past forward to the present to the knowledge of the speaker.
Simple Past Tense
The simple past tense:
The simple past is a verb tense that is used to talk about things that happened or existed before now.
"Stood" identifies an action that happened in the past that was completed in the past. There is no expectation that the action continued beyond that moment of the past. "He stood there, then he left," is an example of an action in the past that was completed in the past.
Summary of the differences
The progressive past tense is used when you know the action continued beyond the time in the past you're talking about.
She was flying to Venice for a vacation when her brother won the lottery. (The act of flying continues beyond the act of winning the lottery).
The simple past tense is used when you know the action was completed in the past.
She flew to Venice for a vacation and didn't know her brother won the lottery. (The act of flying was completed without knowing about winning the lottery.)
And concerning your examples
The amount of sales was standing at $10000 in 1990.
The above sentence (progressive past tense) means the amount of sales in 1990 was $10,000 and continued to be $10,000 into the future beyond 1990 until something acts to modify the condition (the state of being $10,000).
The amount of sales stood at $10000 in 1990.
The above sentence (simple past tense) means the amount of sales in 1990 was $10,000 but it may not have stayed at $10,000. The value may have changed later.
