1. I have been writing six letters since morning.
  2. I have written six letters since morning.
  • 2
    It depends. Are you done writing the letters or not? – John Feltz Jan 7 '17 at 16:24
  • 2
    Dear_digvijit_, our community looks for useful questions and answers which may be searched by other students later. As our site is frequently accessed by non-users who may be having the same questions, we try to keep it organized and provide all necessary informations so that other students may also be aware of it. Increase more details to your question, why are you confused? Have you tried to look up the differences between present perfect tense and present perfect continous? If you have and still are confused, come back here and provide more informations otherwise your answer may be closed. – Davyd Jan 7 '17 at 16:40

Depending on the situation, either 1 or 2 could be correct.

If you started writing these six letters in the morning and are still writing them, then you use the first variant.

If you've already finished writing the letters by this time, then you use the second.

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