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میتونی لایو بذاری!

A committee of 6 people, which must contain at least 4 men and at least 1 woman, is to be chosen from 10 men and 9 women.

a) Find the number of possible committees that can be chosen.

b) Find the probability that one particular man, Albert, and one particular woman, Tracey, are both on the committee.

c) Find the number of possible committees that include either Albert or Tracey but not both.

d) The committee that is chosen consists of 4 men and 2 women. They queue up randomly in a line for refreshments. Find the probability that the women are not next to each other in the queue.

پاسخ تشریحی :
نمایش پاسخ

a) $4M{\text{ }}2W$ or $5M{\text{ }}1W$

chosen in ${}^{10}{C_4} \times {}^9{C_2} + {}^{10}{C_5} \times {}^9{C_1}$

$ = 9828$

b) ${}^9{C_3} \times {}^8{C_1} + {}^9{C_4} = 798$

Prob $ = 798/9828 = 0.0812$

c) Albert + not $T...{\text{ }}{}^9{C_3} \times {}^8{C_2} + {}^9{C_4} \times {}^8{C_1}$

$ = 3360$

Tracey + not $A...{\text{ }}{}^9{C_4} \times {}^8{C_1} + {}^9{C_5}$

$ = 1134$

Number of ways $ = 4494$

d) $6! - 4! \times 5 \times 2$ or $6! - 5! \times 2{\text{ }}\left( { = 480} \right)$

OR $4! \times 5 \times 4$ or $4! \times {}^5{P_2}{\text{ }}\left( { = 480} \right)$

prob $ = 480/6! = 2/3{\text{ }}\left( {0.667} \right)$

OR using probabilities…as above

OR Women together $5!/4!{\text{ }}\left( { = 5} \right)$

Women not together $ = 15 - 5 = 10$

total ways $MMMMWW = 6!/4!2! = 15$

prob $ = 2/3$

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