JEE Main & Advanced JEE Main Paper Phase-I (Held on 08-1-2020 Evening)

  • question_answer
    If the 10th term of an A.P. is \[\frac{1}{20}\] and its 20th term is \[\frac{1}{10}\], then the sum of its first 200 terms is [JEE MAIN Held on 08-01-2020 Evening]

    A) \[{{50}^{\frac{1}{4}}}\]                     

    B) \[50\]

    C) \[100\]  

    D) \[{{100}^{\frac{1}{2}}}\]

    Correct Answer: D

    Solution :

    \[\therefore \,\,\,\,\,\,\,\,a+9d=\frac{1}{20}\]         ... (i)       \[a+19d=\frac{1}{100}\]     ?. (ii) \[\therefore \] By (ii)-(i) \[10d=\frac{1}{10}-\frac{1}{20}=\frac{10}{200}=\frac{1}{20}\] \[\Rightarrow \,\,\,\,\,d=\frac{1}{200}\]     \[\Rightarrow \,\,\,\,\,a=\frac{1}{200}from\,\,(i)\] \[\therefore \,\,\,\,\,\,{{S}_{200}}=100\left[ 2\times \frac{1}{200}+\frac{199}{200} \right]\] \[=1+\frac{199}{2}=\frac{201}{2}\]    \[=100\frac{1}{2}\]


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