i continue to have difficulty lay with pretérito vs imperfecto. In the sentence She sang in a rock band in high school, why is it ella cantaba ella

Question

cantó?  I understand it is a repeated action in the past, however it is also during a specific time frame ( high school), which has been completed.  Este me cuesta mucho.  Por favor, ayúdame.  Gracias

Answer

Hola Abby
As you know the Imperfect tense is used to express a repeated action in the past, like the sentence you mentioned. I have changed the translation in English to "used to sing" so it is more clear. 
As you are saying, why not cantó? 
If you see this sentence in English, "She sang in a band during high school", despite having a timeframe that shows the action is a completed action (she is not in high school any more), this can take both the Imperfect and the Indefinido. If you use the imperfect: cantaba, the speaker is seeing "her" singing in the band during her time in high school, with no specific beginning or end. If you use the Indefinido: cantó, the speaker is seeing the action of singing as an action with a clear beginning and an end. 
We appreciate the difference between the Imperfecto and the Indefinido is quite tricky. It needs a lot of practice.
Here is a lesson about this. It is explaining the general difference between these two tenses
https://spanish.kwiziq.com/revision/grammar/using-el-imperfecto-vs-el-indefinido-general-use
I hope this clarifies your doubts.
Un saludo
Inma

Answer

Similar confusion arose with "He trained every day during the competiion. The competion is over. The training period is ended and is a completed series of actions in the past. so preterite would seem appropriate. The question concerning singing has been changed to "used to sing" to make it clearer. Please change "trained" to " Used to train"

Answer

Similar confusion arose with "He trained every day during the competiion. The competion is over. The training period is ended and is a completed series of actions in the past. so preterite would seem appropriate. The question concerning singing has been changed to "used to sing" to make it clearer. Please change "trained" to " Used to train"

Answer

I, too, am having trouble with the quiz questions. "How would you say "The tennis player trained every day during the competitions."? I would translate it with the simple past, not the imperfect. I understand I can use imperfect if I want to emphasize the repetition, but I usually only use it if I want to say something else happened (simple past) while the repeated or ongoing action was happening (before, during and after). So, without some other indication of time frame, I would almost always translate a sentence like this with the simple past. It happened, and it's done.

I also have trouble with the use of "pretérito indefinido" for simple past. Indefinite sounds an awful lot like imperfect.