JEE Advanced Mathematics question
Seven different lecturers are to deliver lectures in seven periods of a class on a particular day. A, B and C are three of the lecturers. The number of ways in which a routine for the day can be made such that A delivers his lecture before B, and B before C, is
Answer: (D)
Solution
Without restriction there are routines. The three lecturers A, B, C can appear in relative orders, all equally frequent, and exactly one of these (A, B, C) is allowed. So the count is
= 840,
w
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