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Two thirds of students in a class are boys and rest girls. It is known that the probability of a girls. It is known that the probability of a girl getting a first grade is 0.85 and that of boys is 0.70. Find the probability that a student chosen at random will get first grade marks.

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The correct Answer is:
`=2/3 xx 0.70 + 1/3 xx 0.85 = (1.4)/(3) + (0.85)/(3) = (2.25)/(3) = 0.75`
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