JEE Main & Advanced Sample Paper JEE Main Sample Paper-19

  • question_answer If 10% of a radioactive material decays in 5 days, then the amount of the original material left after 20 days is approximately

    A)  \[60%\]                        

    B)  \[65%\]

    C)  \[70%\]                        

    D)  \[75%\]

    Correct Answer: B

    Solution :

     Let initial amount be 100 gm.
    disintegrated  Left
    \[100gm\,\xrightarrow{5\,days}\]\[\frac{100\times 10}{100}\] 10 90
    \[90\,\xrightarrow{Next\,5days}\]\[\frac{90\times 10}{100}\] 9 81
    \[81\xrightarrow{Next\,5\,days}\]\[\frac{81\times 10}{100}\] 8.1 \[\approx \,73\]
    \[73\xrightarrow{Next\,5\,days}\]\[\frac{73\times 10}{100}\] \[7.3\] \[\approx \,65\]

adversite


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