JEE Advanced

Question 53

Viewing 2 posts - 1 through 2 (of 2 total)
  • Author
    Posts
  • #11694
    shahkb4
    Keymaster

    Let the mean and variance of 8 numbers

    \[ -10,-7,-1, x, y, 9,2,16 \text { be } \frac{7}{2} \text { and } \frac{293}{4} \text {, respectively. } \]

    Then the mean of 4 numbers $\mathrm{x}, \mathrm{y}, \mathrm{x}+\mathrm{y}+1,|\mathrm{x}-\mathrm{y}|$ is
    [JEE MAIN 23 Jan 2026 S I]
    (1) 11
    (2) 9
    (3) 10
    (4) 12

    #11695
    shahkb4
    Keymaster

    Solution

    \[ \begin{aligned} & \text { Mean }=\frac{\sum x_{i}}{8}=\frac{-10-7-1+x+y+9+2+16}{8}=\frac{7}{2} \\ & \Rightarrow x+y=19 \quad \ldots(1) \\ & \text { Variance }=\frac{1}{n} \sum x_{i}^{2}-\mu^{2}=\frac{293}{4} \\ & =\frac{1}{8}\left(100+49+1+x^{2}+y^{2}+81+4+256\right)-\left(\frac{7}{2}\right)^{2}=\frac{293}{4} \end{aligned} \]
    \[ \begin{aligned} & \Rightarrow x^{2}+y^{2}+406+85=8\left[\frac{49+293}{4}\right]=684 \\ & \Rightarrow x^{2}+y^{2}=684-491=193 \text { from }(1) \\ & \Rightarrow x^{2}+(19-x)^{2}=193 \\ & \Rightarrow(x-12)(x-7)=0 \\ & x=12 \mid x=7 \\ & y=7 \mid y=12 \end{aligned} \]

    required numbers $\mathrm{x}, \mathrm{y}, \mathrm{x}+\mathrm{y}+1,|\mathrm{x}-\mathrm{y}|$ are 12, 7, 20, 5

    \[ \text { Mean }=\frac{12+7+20+5}{4}=11 \text { Answer }(1) \]
Viewing 2 posts - 1 through 2 (of 2 total)
  • You must be logged in to reply to this topic.