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SSC Sample Paper Mock Test-10 SSC CGL Tear-II Paper-1

  • question_answer
    If the 4th term of an arithmetic progression is 14 and the 12th term is 70, then the first term is

    A)  \[-10\]  

    B)  \[-7\] 

    C)  \[+7\]

    D)  \[+10\]

    Correct Answer: B

    Solution :

      \[{{a}_{4}}={{a}_{1}}+(4-1)\times d\] \[14={{a}_{1}}+3d\]                            \[\Rightarrow \]   \[{{a}_{1}}=14-3d\]                              ?(i) \[70={{a}_{1}}+11d\]                          ?(ii) After putting the value of a, in Eq. (ii), we get \[14-3d+11d=70\] \[\Rightarrow \]               \[8d=70-14\]\[\Rightarrow \]\[d=7\] \[\therefore \] \[{{a}_{1}}=14-21=-7\]


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