Geraldine Tan's answer to Cqviezel Liow's Junior College 2 H2 Maths question.
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OKOK I GOT IT
first part need consider by case
i. group two sis tgt, then from 12 seats you choose 1 for the sis group (12C1) then ×2 cause the sis can swap places so left with 10 seats for the 6 others to choose (10C6), then can arrange 6 others (6! since each seat is numbered)
ii. out of 12 seats you blank out two for sis, so left 10 for 6 people to choose (10C6) and arrange these 6 people (6!), then you slot in 1 sis between any of the people (6C1) then ×2 for the sis to swap places
first part need consider by case
i. group two sis tgt, then from 12 seats you choose 1 for the sis group (12C1) then ×2 cause the sis can swap places so left with 10 seats for the 6 others to choose (10C6), then can arrange 6 others (6! since each seat is numbered)
ii. out of 12 seats you blank out two for sis, so left 10 for 6 people to choose (10C6) and arrange these 6 people (6!), then you slot in 1 sis between any of the people (6C1) then ×2 for the sis to swap places
Date Posted:
6 years ago
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