JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2013

  • question_answer
        If n arithmetic means are inserted between two sets of numbers\[a,2b\]and\[2a,b\]where \[a,b\in R\]suppose mth mean between these two sets of numbers is same, then the ratio \[a:b\]equals to

    A)  \[n-m+1:m\]                    

    B)  \[n-m+1:n\]

    C)  \[m:n-m+1\]                    

    D)  \[n:n-m+1\]

    Correct Answer: C

    Solution :

                    Since, n arithmetic means are inserted between a and 2b, \[\therefore \] \[{{a}_{m}}\] (mth mean) \[=a+\frac{m}{n+1}(2b-a)\] and n arithmetic means are inserted between 2a and b. \[\therefore \]\[a{{}_{m}}\](mth mean) \[=2a+\frac{m}{n+1}(b-2a)\] Given,   \[{{a}_{m}}=a{{}_{m}}\] \[\Rightarrow \]\[a+\frac{m}{n+1}.(2b-a)=2a+\frac{m}{(n+1)}(b-2a)\] \[\Rightarrow \]               \[\frac{a}{b}=\frac{m}{n-m+1}\] \[\therefore \]  \[a:b=m:n-m+1\]


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