- #1
Matejxx1
- 72
- 1
Homework Statement
The chance that an event A will happen is always equal to 0,3. We stop the experiment once event A occurs What is the probability that :
a) we have to attempt the even at least 4 times
b)we then do the event a fourth time
I am asking this because the professor did not tell us the answers for the problems because he wanted us to solve this ourselfs
Homework Equations
A=event
A'= complemetary event
The Attempt at a Solution
a)
ok so here I was thinking that if the event has to occur at least 4 times that means that the event A fails to occur the first 3 times. therefore I tried writting it like this
P(A)+P(A')=1
P(A)=1-P(A')
P(A)=1-(0,7*0,7*0,7) fails the first 3 times
P(A)=0,657=66%
What I was trying to do here was to find what are the chances that the experiment will fail the first 3 times, and then I just substracted that from 1 (1 meaing that the event is 100% sure to happen)
b)we then do the event a fourth time
I was thinking that this means , that the event succeded the 3 time and then for some reason we repeat the event a 4 time
I tried solving this one like this :
P(A'A'AA+A'A'AA')...... A= A has happened A'= A has no happened
the first part demonstrates that the 2 the times the event fails and then the 3 &4 times is succeds , but because we don't know if the 4 th time the event succeds we also have to take into account and check was happends of the event fails
and so if I add those two things up:
P(A)=(0,7*0,7*0,3*03+0,7*0,7*0,3*0,7)
P(A)=0,*72*0,3(0,3+0,7)
P(A)=0,72*0,3(1)
P(A)=0,15=15%
thanks