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Railways NTPC (Technical Ability) Tool Engineering Question Bank Tool Engineering

  • question_answer
    A PERT network has three activities on critical path with mean time 3, 8 and 6, and standard deviation 1, 2 and 3 respectively. The probability that the project will be completed in 20 days is:

    A) 0.50                             

    B) 0.79

    C) 0.84                             

    D) 0.95

    Correct Answer: B

    Solution :

    Standard derivation, \[\sigma ={{1}_{2}}+{{2}_{2}}+{{3}_{2}}=3.7416\] \[{{T}_{m}}=3+8+6=17\,days\] \[{{T}_{s}}=20\,days\] Probability of waiting, \[z=\frac{{{T}_{s}}-{{T}_{m}}}{\sigma }=0.802\] For \[z\text{ }=\text{ }0.802,\] area under the normal distribution curve  \[=\text{ }0.7881\text{ }=\text{ }0.79\]


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