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June 2018 p62 q6
2830
Donna has 2 necklaces, 8 rings and 4 bracelets, all different. She chooses 4 pieces of jewellery. How many possible selections can she make if she chooses at least 1 necklace and at least 1 bracelet?
Solution
To solve this problem, we need to calculate the number of ways to choose 4 pieces of jewellery such that at least 1 necklace and at least 1 bracelet are included.
Calculate the total number of ways to choose 4 pieces from 14 items (2 necklaces + 8 rings + 4 bracelets) and subtract the cases where there are no necklaces or no bracelets:
Total ways:
\(\binom{14}{4} = 1001\)
Subtract cases with no necklaces (only rings and bracelets):
\(\binom{12}{4} = 495\)
Subtract cases with no bracelets (only necklaces and rings):
\(\binom{10}{4} = 210\)
Subtract cases with only rings:
\(\binom{8}{4} = 70\)