prob q hard! (1 Viewer)

[StGeorgeDragons]

the letters of the word BANANAS are written on separate cards and drawn at random from a hat. calculate the probability that : an A will be drawn first or last but not both

 

[klaw]

P(A drawn first or last)= P(A drawn first but not last)+P(A drawn last but not first)=3/7*2/3+4/7*1/2=4/7

 

[haboozin]

P(A drawn first or last)= P(A drawn first but not last)+P(A drawn last but not first)=3/7*2/3+4/7*1/2=4/7

sorry that is not the right answer

 

[currysauce]

bugger

How is it done then?

 

[haboozin]

i'll have a crack at it, even tho i am hopeless at perms

overall probability = 7! / 3!2!

Lets see, umm If you have A at the start, then 5 other positions can be filled 5!/2!2! then you x 2? for the reverse, if the A is at the end (i really got no clue)

therefore

5!/2!2! // 7!/3!2! = 30/420 = 3/42 = 1/14?

sorry wrong....


.........................

 

[jemsta]

do you have the answer for it coz i wanna see if i got it right before posting the steps

 

[haboozin]

do you have the answer for it coz i wanna see if i got it right before posting the steps

Klaw was close...

if i give the answer then u'll easily think of a way of producing it..

if your answer wasnt kinda like Klaws then its wrong.


oh and im not sure how its done sorry

 

[souha882002]

Is It 48/7 ?

 

[klaw]

Is It 48/7 ?

can't be, that means there's a 686% chance of happening

 

[souha882002]

OOOPPPSS.....that is completely wrong....it cant be greater than 1. Oh well, ill just try it again.

 

[jake2.0]

is the answer 4/9????

 

[klaw]

how did you get 4/9?

 

[jake2.0]

i wanna know if its right first, don't wanna look like an idiot!

 

[souha882002]

i cant see why KLAW'S answer is wrong. Ive tried it tonnes of ways, but Klaw's way is the only one that makes sense? Maybe the original answer is wrong..........

 

[klaw]

I can't see what I did wrong either

 

[jake2.0]

does any1 have the answer??

 

[speed2]

i got 4/9 aswell

 

[serge]

did anyone get 390/480=13/16?

 

[Pace_T]

is it 16/21? lol

 

[speed2]

ok here's how i did it;

for A at start not at end

there are 7 spaces to be filled
for the 1st space it has to be 1 of the A's so 3/7
the last space can be filled by any of the remaining letters except the A's so 4/6
so total probability for A at start not at end is 3/7.4/6=2/7

you just double that for the other way; A at end not at start

hope thats right