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Question 612870: From a class of girls and boys, the probability that one student chosen at random will be a boy is 2/3. If 3 girls leave the class, the probability that a student chosen at random will be a boy is 4/5. How many boys and girls are ther in the class before the 3 girls leave?
Thanks !
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! From a class of girls and boys, the probability that one student chosen at random will be a boy is 2/3. If 3 girls leave the class, the probability that a student chosen at random will be a boy is 4/5. How many boys and girls are ther in the class before the 3 girls leave?
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P(b) = 2/3
b/(b+g) = 2/3
3b = 2b+2g
b = (2/3)b + (2/3)g
(1/3)b = (2/3)g
b = 2g
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Equation:
b/(b + g-3) = 4/5
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(2g)/(2g + g-3) = 4/5
10g = 4(3g-3)
10g = 12g-12
2g = 12
g = 6 (original # of girls)
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b = 2g = 12 (original # of boys)
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Cheers,
Stan H.
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