KVPY Sample Paper KVPY Stream-SX Model Paper-13

  • question_answer
    Let \[[x]\] and \[\{x\}\] be the integral part and fractional part of a real number x respectively. Then the value of the integral  \[\int_{0}^{5}{[x]\{x\}dx}\] is

    A) \[\frac{5}{2}\]

    B) \[5\]

    C) \[\frac{69}{2}\]

    D) \[\frac{71}{2}\]

    Correct Answer: B

    Solution :

    Let \[I=\int_{0}^{5}{[x]\{x\}dx}\]
    \[\Rightarrow \]   \[I=\int_{0}^{1}{\{0\}dx}+\int_{1}^{2}{\{x\}dx+2\int_{2}^{3}{\{x\}dx}}\]\[+\,3\int_{3}^{4}{\{x\}dx+\int_{4}^{5}{4\{x\}dx}}\]
    \[\Rightarrow \]   \[I=(1+2+3+4)\int_{0}^{1}{x\,dx}\] [\[\because \{x\}\]is periodic with 1]
    \[\Rightarrow \]   \[I=10\left[ \frac{{{x}^{2}}}{2} \right]_{0}^{1}\]
    \[I=\frac{10}{2}=5\]


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