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The variance value for an F-distribution with parameters V1 = 5 and V2 = 9 is :

  • A.1.587
  • B.1.378
  • C.2.578
  • D.1.498

Answer: A

The variance is 1.587.

For an F-distribution with \(\nu_{1}\) and \(\nu_{2}\) degrees of freedom (here 5 and 9; the variance exists only when \(\nu_{2}\) is greater than 4):

\[ \begin{aligned} V &= \frac{N}{D} \\ N &= 2\nu_{2}^{2}(\nu_{1} + \nu_{2} - 2) \\ D &= \nu_{1}(\nu_{2} - 2)^{2}(\nu_{2} - 4) \end{aligned} \]

\[ \begin{aligned} V &= \frac{2(81)(12)}{5(49)(5)} \\ &= \frac{1944}{1225} = 1.587 \end{aligned} \]

The mean of this distribution is \(\nu_{2}/(\nu_{2} - 2) = 9/7 = 1.286\), which none of the options gives; 1.378, 2.578 and 1.498 do not follow from the formula.

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