Deconstructing the QuestionWe need the value of
\(n\), the number of males in a group of
\(5\).
So the number of females is
\(5-n\).
This is a Data Sufficiency question, so the goal is to determine whether each statement gives one unique value of
\(n\).
The key ideas are direct translation in statement (1) and complement counting in statement (2).
Step-by-stepFrom the question stem, males are
\(n\) and females are
\(5-n\).
Statement (1): The number of males in the group is one more than the number of females.
This gives:
\(n=(5-n)+1\)So:
\(n=6-n\)\(2n=6\)\(n=3\)This gives one unique value of
\(n\).
Statement (1): SufficientStatement (2): The probability the team consists of at least one male is
\(\frac{9}{10}\).
Use the complement.
If the probability of at least one male is
\(\frac{9}{10}\), then the probability of all females is:
\(1-\frac{9}{10}=\frac{1}{10}\)The total number of 2-person teams from 5 people is:
\(\frac{5!}{2!3!}=10\)So the number of all-female teams must be
\(1\).
If there are
\(5-n\) females, then:
\(\frac{(5-n)!}{2!(3-n)!}=1\)The number of ways to choose 2 people is 1 only when there are exactly 2 females.
So:
\(5-n=2\)\(n=3\)This also gives one unique value of
\(n\).
Statement (2): SufficientAnswer: D