arthham

JEE Advanced 2016 · Permutations and Combinations

A debate club consists of 66 girls and 44 boys. A team of 44 members is to be selected from this club including the selection of a captain (from among these 44 memers) for the team. If the team has to include at most one boy, then the number of ways of selecting the team is

Answer: A. 380380

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Written solution

Given: 6 girls, 4 boys\text{Given: } 6 \text{ girls},\ 4 \text{ boys}

Team: 4 members+1 captain (from the 4)\text{Team: } 4 \text{ members} + 1 \text{ captain (from the } 4)

Condition: at most one boy\text{Condition: at most one boy}

To find: number of ways of selecting the team\text{To find: number of ways of selecting the team}

Plan: count valid teams (0 boy / 1 boy), then the captain\text{Plan: count valid teams (0 boy / 1 boy), then the captain}

Captain: 1 from the team of 4⇒4 ways per team\text{Captain: } 1 \text{ from the team of } 4 \Rightarrow 4 \text{ ways per team}

Total=4×(#valid teams)\text{Total} = 4 \times (\#\text{valid teams})

Case 0 boys: (64)=15\text{Case 0 boys: } \binom{6}{4} = 15

Case 1 boy: (41)(63)=4×20=80\text{Case 1 boy: } \binom{4}{1}\binom{6}{3} = 4 \times 20 = 80

#valid teams=15+80=95\#\text{valid teams} = 15 + 80 = 95

Each team→4 captain choices\text{Each team} \to 4 \text{ captain choices}

Total=95×4=380\text{Total} = 95 \times 4 = 380

Check (captain first): 6[(53)+(41)(52)]=6(10+40)=300\text{Check (captain first): } 6\left[\binom{5}{3}+\binom{4}{1}\binom{5}{2}\right] = 6(10+40)=300

4(63)=4×20=80⇒300+80=3804\binom{6}{3}=4\times 20=80 \Rightarrow 300+80=380

380Option (1)\boxed{380}\quad\text{Option (1)}

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