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  • Rewarding $1$ mark has the Probability = $\frac{1}{4}$
  • Rewarding $-0.25$ mark has the Probability = $\frac{3}{4}$

Hence, expected value for one question = $1*\frac{1}{4} + \left ( -0.25 \right )*\frac{3}{4} = \frac{1}{16}$ 

Hence, Total expectation for $80$ questions = $\frac{1}{16} *80 = 5$ ?

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