help in h2 maths probability.

• lavastar

  26 Apr 08, 18:32

  1.Assume that the probability of a person being born in any month of the year to be 1/12. calculate the probability that of 4 randomly chosen people, exactly two will have birthday in the same month and the other two are in different months. (ans : 0.382)
  
  2.Four boys and three girls stand in a queue in random order. Find the probability that all 4 boys stand next to each other given that at least 3 boys stand next to each other. (ans : 0.25)
  
  3.Eleven cards bearing the letters of the world INDEPENDENT are placed in a box. Three cards are drawn at random without replacement. Calculate the probability that i) exactly 2 of the cards bear same letters. ans:16/55 ii) all three cards bear different letters. ans:116/165
  
  Thx for those who can help  i try a few times still cnt get the answer..

• eagle

  26 Apr 08, 22:30

  1) I lazy to do at the moment... but hint for question 1:

  

  and remember, they are independent events, so you sum them up
  

• dumbdumb!

  26 Apr 08, 22:47

  i'm studying probability too.. mine is more difficult though.

   

  need a little help too.

• FirePig

  27 Apr 08, 14:19

  Keep doing until you get the answers lor...at least you have the answers. Exams no answer.

  I wont be doing these until my exams are over.

• weewee

  28 Apr 08, 22:39

  Originally posted by lavastar:

  1.Assume that the probability of a person being born in any month of the year to be 1/12. calculate the probability that of 4 randomly chosen people, exactly two will have birthday in the same month and the other two are in different months. (ans : 0.382)
  
  2.Four boys and three girls stand in a queue in random order. Find the probability that all 4 boys stand next to each other given that at least 3 boys stand next to each other. (ans : 0.25)
  
  3.Eleven cards bearing the letters of the world INDEPENDENT are placed in a box. Three cards are drawn at random without replacement. Calculate the probability that i) exactly 2 of the cards bear same letters. ans:16/55 ii) all three cards bear different letters. ans:116/165
  
  Thx for those who can help  i try a few times still cnt get the answer..

  Q1) first person can have birthday on any month with probability 1

  second person probability 1/12

  third person prob 11/12

  fourth person prob 10/12

  The first person can have his birthday on any month. 3! ways of arrangement.

  Therefore, 1*1/12*11/12*10/12*3!=0.382

   

  I cheated. From the answer, i work backwards to get the idea.