Half-lives of two radioactive elements $A$ and $B$ are $20$ minutes and $40$ minutes, respectively. Initially, the samples have equal number of nuclei. After $80$ minutes, the ratio of decayed number of $A$ and $B$ nuclei will be

  • [JEE MAIN 2016]
  • A

    $1 : 4$

  • B

    $5 : 4$

  • C

    $1 : 16$

  • D

    $4 : 1$

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