Probabilities from a quadratic density function and the distribution and expectation of its rounded value

Probabilities from a quadratic density function and the distribution and expectation of its rounded value

IB Year 6 | Grade 12
7 marks

The probability density function of a continuous random variable \(X\) is \(f\), where

\[f(x)=\begin{cases}\frac{3}{16}x(4-x), & 0\leq x\leq2,\\ 0, & \text{otherwise}.\end{cases}\]

  1. Find \(P(0.5\leq X<1.5)\).[2]
  2. The discrete random variable \(Y\) is obtained by rounding \(X\) to the nearest whole number. Its probability distribution is given in the table below.[3]
    \(y\)\(0\)\(1\)\(2\)
    \(P(Y=y)\)\(a\)\(b\)\(c\)
    1. Write down \(b\).
    2. Find \(a\) and \(c\).
  3. Find \(E(Y)\).[2]

Solution:

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Answer:(a) \(\dfrac{35}{64}\) (b)(i) \(b=\dfrac{35}{64}\) (b)(ii) \(a=\dfrac{11}{128},\ c=\dfrac{47}{128}\) (c) \(\dfrac{41}{32}\)

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