Given that x1,x2,x3,…,x10x_1, x_2, x_3, \dots, x_{10} are 10 unique numbers whose mean, xˉ\bar{x}, is 11.8 and standard deviation is 4.729. Find the value of

  1. ((i))

    $x_1 + x_2 + x_3 + \dots + x_{10}\

    Answer -------------------------------

  2. ((ii))

    x12+x22+x32+⋯+x102x_1^2 + x_2^2 + x_3^2 + \dots + x_{10}^2, giving your answer to the nearest whole number.\

    Answer -------------------------------

  3. ((iii))

    Each of the value of xnx_n is changed as follows:

    If xn<xˉx_n < \bar{x}, then xnx_n is decreased by 2.
    If xn>xˉx_n > \bar{x}, then xnx_n is increased by 2.

    Explain clearly, how this would affect the value of the standard deviation.

    Answer ___

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Worked solution

15((i))

1. Use the mean formula to find the sum of the 10 numbers.

xˉ=x1+x2+x3+⋯+x1010\bar{x}=\frac{x_1+x_2+x_3+\cdots+x_{10}}{10}
Given xˉ=11.8\bar{x}=11.8,
x1+x2+x3+⋯+x10=10(11.8)=118x_1+x_2+x_3+\cdots+x_{10}=10(11.8)=118

Answer

118118

15((ii))

1. Write the standard deviation formula and substitute the given values.

For n=10n=10, xˉ=11.8\bar{x}=11.8 and standard deviation =4.729=4.729,
4.729=x12+x22+⋯+x10210−11.824.729=\sqrt{\frac{x_1^2+x_2^2+\cdots+x_{10}^2}{10}-11.8^2}

2. Rearrange the formula and calculate the sum of squares.

Squaring both sides,
4.7292=x12+x22+⋯+x10210−11.824.729^2=\frac{x_1^2+x_2^2+\cdots+x_{10}^2}{10}-11.8^2
Hence
x12+x22+⋯+x102=10(4.7292+11.82)x_1^2+x_2^2+\cdots+x_{10}^2=10(4.729^2+11.8^2)
=10(22.363441+139.24)=10(22.363441+139.24)
=1616.03441=1616.03441
To the nearest whole number,
x12+x22+⋯+x102=1616.x_1^2+x_2^2+\cdots+x_{10}^2=1616.

Answer

16161616

15((iii))

1. Identify how the transformation changes each value's distance from the mean.

For any value below the mean, xn<xˉx_n<\bar{x}, decreasing it by 2 makes it even further below xˉ\bar{x}.
For any value above the mean, xn>xˉx_n>\bar{x}, increasing it by 2 makes it even further above xˉ\bar{x}.

2. Conclude the effect on the standard deviation.

Since the data values become more spread out from the mean, the standard deviation becomes larger.

Answer

The standard deviation would increase, because each value is moved further away from the mean, increasing the spread of the data.

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