In a certain laboratory, chemicals are identified by a colour-coding system. There are 20 different chemicals. Each one is coded with either a single colour or a unique two-colour pair. If the order of colours in the pairs does not matter, what is the minimum number of different colours needed to code all 20 chemicals with either a single colour or a unique pair of colours?
A. 7
B. 6
C. 5
D. 8
Answer: Option B
Solution(By Examveda Team)
Each one coded with either a single colour or unique two-colour pair.Therefore, total number of ways = n + nC2
Minimum number of different colour needed to code all 20 chemicals will be 6
= 6 + 6C2
=21
Related Questions on Permutation and Combination
A. 3! 4! 8! 4!
B. 3! 8!
C. 4! 4!
D. 8! 4! 4!
A. 7560,60,1680
B. 7890,120,650
C. 7650,200,4444
D. None of these
A. 8 × 9!
B. 8 × 8!
C. 7 × 9!
D. 9 × 8!
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