Я записал номер в тетрадь.

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Breakdown of Я записал номер в тетрадь.

• в: in
• записать: to write down
• тетрадь: the notebook

Questions & Answers about Я записал номер в тетрадь.

Why is it записал, not just писал or написал?

Russian has many verbs of writing, and aspect matters:

• писать (imperfective) = to write (in general, be writing)
  
  • я писал номер – I was writing the number / I used to write the number (process or repeated action, not a finished single result).
• написать (perfective) = to write (and finish some text)
  
  • я написал номер – usually sounds like I wrote the number (somewhere) but with more focus on the act of writing itself, not on storing/recording it.
• записать (perfective) = to write something down, to note it, to record it
  
  • Emphasizes recording for later use (not just writing shapes).

In Я записал номер в тетрадь, the speaker is saying they wrote the number down (to keep it), which is exactly the nuance of записать.

Why is it записал and not something like записалИ or записало?