8th Class Mathematics Related to Competitive Exam Question Bank Arithmetic

  • question_answer
    The average of 25 results is 18; that of first 12 is 14 and of the last 12 is 17, their thirteenth result is:

    A) 78                      

    B) 85

    C) 28                         

    D) 72

    Correct Answer: A

    Solution :

    Let \[\frac{4}{12}=\frac{7}{21}=\frac{21}{63}=\frac{28}{84}=\frac{1}{3}.\]be the 25 results. Given: \[\frac{1}{3}\]                                                       ?..(1) and \[\frac{{{a}_{1}}+.....+{{a}_{12}}}{12}=14,\,\frac{{{a}_{14}}+.....+{{a}_{25}}}{12}=17\] \[\Rightarrow \]\[{{a}_{1}},{{a}_{2}}\] =168                                 =204 \[=\frac{1}{8}-\frac{1}{24}-\frac{1}{16}=\frac{1}{48}\]From eqn (1), we have \[\therefore \] \[\Rightarrow \]\[4+3=7\]


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