The average marks of Sameer decreased by $1,$ when he replaced the subject in which he has scored $40 \,marks$ by the other two subjects in which he has just scored $23$ and $ 25$ marks respectively. Later he has also included $57$ marks of Computer Science, then the average marks increased by $2.$ How many subjects were there initially?

  • A

    $6$

  • B

    $12$

  • C

    $15$

  • D

    $9$

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