If the first, second and last terms of an $A.P.$ be $a,\;b,\;2a$ respectively, then its sum will be

  • A

    $\frac{{ab}}{{b - a}}$

  • B

    $\frac{{ab}}{{2(b - a)}}$

  • C

    $\frac{{3ab}}{{2(b - a)}}$

  • D

    $\frac{{3ab}}{{4(b - a)}}$

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