Решение задачи N2834 теория вероятностей

2834. In the group of 30 students. In the control work, 5 people received marks "excellent", 10 people - "good", 10 people - "satisfactory". What is the likelihood that all three students brought to the blackboard have unsatisfactory marks on the test?

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