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GATE 2021 CS – Question 64

Engineering Mathematics · Probability and Statistics · 2 marks · Numerical answer

A sender (S) transmits a signal, which can be one of the two kinds: $H$ and $L$ with probabilities 0.1 and 0.9 respectively, to a receiver (R). In the graph below, the weight of edge $(u,v)$ is the probability of receiving $v$ when $u$ is transmitted, where $u,v\in\{H,L\}$. The edge weights are: H to H = 0.3, H to L = 0.7, L to H = 0.8, L to L = 0.2. If the received signal is $H$, the probability that the transmitted signal was $H$ (rounded to 2 decimal places) is ______.

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Correct answer: 0.04

Explanation

Bayes: P(H sent | H received) = (0.1 x 0.3)/(0.1 x 0.3 + 0.9 x 0.8) = 0.03/0.75 = 0.04.