Seven different lecturers are to deliver lectures in seven periods of a class on a particular day. A, B, C are the three lecturers. The number of ways in which the routine for the day can be made such that A delivers his lecture before B and B before C is-
a) 420
b) 120
c) 210
d) 840
Answers
A,B,C take their places in 7C3 =35 ways
remaining 4 take their places
in 4! =24ways
total =35x24=840
840 Ways in which the routine for the day can be made such that A delivers his lecture before B and B before C if Seven different lecturers are to deliver lectures in seven periods of a class on a particular day
Step-by-step explanation:
There are total 7 Lectures
A , B & C will deliver 3 Lectures
as order is A delivers his lecture before B and B before C
Hence 3 Lectures out of 7 lectures can be selected in
⁷C₃ = 35 Ways
Remaining 4 Lectures and 4 Lecturers can be arranged in
⁴P₄ = 4! = 24 Ways
Total Ways = 35 * 24 = 840
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