Some probability qu's... i hate this topic. (1 Viewer)

[currysauce]

Lisa had 3 keys in her pocket. To open fer door she tried the keys at random. She stopped trying when she opened the door. She did not ttry the same key 2wice. Find the prob that:

i) the door opened first time

1/3

ii) she tried all 3 keys b4 it opened.

i got FAIL FAIL OPEN

2/3 x 1/2 x 1 = 1/3

 

[Trev]

You answered the question yourself? Or are you asking if they are correct?!
They look alright to me. Though, I thoroughly hate probability also!

 

[currysauce]

haha sorry, yeah i wanted some checking!

Also new question

In a race between brenda and andrea, the prob. of each winning is 0.6 and 0.4 respectively. If they race 3 times, what is the prob. that:

i) Andrea loses a particular race

so i got

P(BBA)+ P(BAB) +P(ABB) = 0.432

ii) Brenda Wins more races than andrea

same + P(BBB)

iii) Andrea wins at least 1

1 - P(BBB) = 0.784

 

[Estel]

For i), I interpreted the q differently and got 0.6
hmm

 

[Trev]

Once again currysauce, it's looking good! lol

 

[currysauce]

god i hate prob.

 

[currysauce]

estel, i went if brenda wins, then andrea loses

so for her to lose a particular race, then its WIN WIN LOSE or aab aba and baa etc..

 

[Trev]

I think he would have realised!
He is aiming for 100 in extension 1. lol...
*silence*

 

[currysauce]

lol

I got an even harder question, wll i reckon lol.


Urn A contains 5 black and 3 white balls while urn B contains 2 black balls and 7 white balls. A person selects either of the urns at random and takes 2 balls without replacement.

By the use of a tree diagram determine the prob. that the balls selected are of the same colour.

 

[Estel]

I maintain my different interpretation of the q... (probability he loses a PARTICULAR race is 0.6... i.e. P(lose 1st race) = 0.6, P(lose 2nd race)= 0.6, etc... ahh well)

Screw tree diagram:
P(same colour) = P(BB + WW)
= (1/2[5C2 + 3C2])/8C2 +(1/2[7C2 + 2C2])/9C2