Number System
A box contains 5 red, 4 black and 4 blue balls. If 3 balls are drawn randomly from the box, what is the probability that there are exactly 2 blue balls in the three drawn balls ?

28/144
29/145
27/143
30/146

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Number System
There are seven boys and four girls in a row. In how many ways can they be seated in the row so that all the girls do not sit together ?

11! - 8! x 3!
11! - 7! x 4!
10! - 7! x 3!
11! - 8! x 4!

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