Mong Chang Hsi's answer to Bryan Tan Jia Jun's Junior College 1 H2 Maths question.

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Mong Chang Hsi
Mong Chang Hsi's answer
39 answers (Tutor Details)
1st
Correct me if I'm wrong

For part i, by doing 5C1 x 4C1 you are double counting the situation as your 5C1 could be Couple A and 4C1 could be Couple B. Another situation could be 5C1 is Couple B and 4C1 be Couple A. Thus you are double counting.