2. Sample Papers
  3. Railways

Railways Sample Paper RRBs Assistant Loco Pilot and Technician CBT STAGE-I Sample Paper-32

  • question_answer
    The sum of the first 20 terms of the series\[\frac{1}{5\times 6}+\frac{1}{6\times 7}+\frac{1}{7\times 8}+...\]

    A)  0.16                

    B)  1.6

    C)  16                   

    D)  0.016

    Correct Answer: A

    Solution :

    First term\[=\frac{1}{5\times 6}=\frac{1}{5}-\frac{1}{6}\] Second term\[=\frac{1}{6\times 7}=\frac{1}{6}-\frac{1}{7}\] 20th term \[=\frac{1}{24\times 25}=\frac{1}{24}-\frac{1}{25}\] \[\therefore \]Required sum \[=\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{24}-\frac{1}{25}\] \[=\frac{1}{5}-\frac{1}{25}=\frac{5-1}{25}=\frac{4}{25}=0.16\]


You need to login to perform this action.
You will be redirected in 3 sec spinner