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HKIMO 2018 Grade 9 National Final (Heat) Set 03 Question 5

HKIMO · HKIMO 2018 Grade 9 National Final (Heat) Set 03

Question 5

A box contains 15 red socks, 21 white socks and 17 blue socks. What is the least number of blindly drawn socks guaranteeing 2 nonwhite pairs and 2 nonred pairs? Each pair uses two socks of the same colour.