Cumulative distribution function of a DRV

Cumulative distribution function of a DRV

IB Year 6 | Grade 12

The probability distribution of a discrete random variable \(X\) is given by \(\mathrm{P}(X = x) = k\left(\frac{2}{3}\right)^x\)

where \(x = 0, 1, 2, 3, \dots\)

  1. Show that \(\mathrm{P}(X \leq x) = 3k\left[1 - \left(\frac{2}{3}\right)^{x+1}\right]\), where \(x = 0, 1, 2, 3, \dots\)
  2. Hence or otherwise, find the value of \(k\).

Solution:

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Answer:(a) \(\mathrm P(X\le x)=3k\left[1-\left(\dfrac23\right)^{x+1}\right]\), \(x=0,1,2,\ldots\) (shown). (b) \(k=\dfrac13\).

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