questions in probability

[sunny2009]

there are 3 women on d platform of a train station.the train that they r waiting for has 5 coaches and each of them is equally likely to enter any coach.what is the probability that they will all enter the same coach?

[duck]

Hi Sunny.. :)

Try to use the basic formula for calculating probability which is = Favorable cases / Total no. of cases

In this que, Total number of ways= 5*5*5
(as each women can entry any of the 5 coaches)

Favorable Cases: 5
(Hint: let suppose, A,B,C,D,E are five different coaches then, favorable cases would be>
AAA , BBB, CCC, DDD, EEE.)

Therefore, probability= 1/25

[sunny2009]

thank u so much duck..:)
        here is another question...i need ur help...
TWO patients share a hospital room for 2 days.suppose that,on a given day,a person independently picks up an airborne disease with probability 1/4.An individual who is infected on d first day will certainly pass it to the other patient on d second day.once contracted,d infection stays at least two days.what is d probability that both d patients have contracted the infection by d end of the second day?

[duck]

Hi Sunny.. :)

Try using this>
Both of them will contract the  infection if
(a) any of them contracted it on the first day. (1/4*3/4) + (1/4*3/4)
[As there are two individuals]
(b) both of them contracted on the first day.(1/4*1/4)
(c)none of them contracted on the first day but both of them contracted on the second day.
(3/4*3/4*1/4*1/4)
 
Add all these , you'll get 121/256

[sunny2009]

hello duck..:)
                i tried very hard over this problem but could not go beyond step C above.coul not think d idea that both of d patients could have contracted d disease on d 2nd day also,thats why i was not reaching d conclusion.
                         thank u so much 4 making my basics in probability clear.i was afraid since i felt probability is not my cup of tea.u r truly genius:):) i will ask for help whenever i will feel problem.

[sunny2009]

jai and vijay are taking a exam in stats.the exam has only 3 grades A,B and C.THE PROBABILITY that jai gets a B is 0.3,the probability that vijay gets a B is 0.4,the probability that neither gets an A,but at least one gets a B is 0.1.what is the probability that neither gets a C but at least one gets a B??
             need help..............how to solve???????????

[Amit Goyal]

Its posted here: Econ sol (Page 5)

[sunny2009]

@amit sir........
        thank u so much sir:)i got it.