Решение задачи N2825 теория вероятностей

2835. In the group of 30 students. 7 students wrote an excellent test, 8 - well, 9 - satisfactorily, the rest received unsatisfactory marks. Find the probability that all 4 students, randomly called to the board, received unsatisfactory marks on the test.

Detailed solution. Decorated in Microsoft Word 2003 (Quest decided to use the formula editor)