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jmc

counting and probability junior

Problem

Our club has 20 members, 10 boys and 10 girls. In how many ways can we choose a president and a vice-president if they must be of the same gender? Assume no one can hold both offices.
Solution
The president can be any one of the 20 members, and the vice-president can be any one of the 9 remaining members of the same sex. The answer is .
Final answer
180