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# probability watch

1. There are n boys in a school.there are 3 girls to every 2 boys.three students are selected at random.the probability that all three selected are boys is 1/30.show that 23n2-114n 88=0
2. (Original post by Rushaanoor15)
There are n boys in a school.there are 3 girls to every 2 boys.three students are selected at random.the probability that all three selected are boys is 1/30.show that 23n2-114n 88=0
We don't give full solutions, only hints. Please post your working so that it can be checked.

There are n boys, so how many pupils are there in total (3:2 girls:boys)?
What is the probability of the first selected pupil being a boy? Second (hint: one fewer to chose from)? Third?
Now equate the product of those to the given answer.
3. The method above does indeed give the stated answer of

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