Respuesta :
Answer:
b) 0.0007
c) 0.4163
d) 0.2375
Step-by-step explanation:
We are given the following:
We treat securities lose value as a success.
P(Security lose value) = 70% = 0.7
Then the securities lose value follows a binomial distribution, where
[tex]P(X=x) = \binom{n}{x}.p^x.(1-p)^{n-x}[/tex]
where n is the total number of observations, x is the number of success, p is the probability of success.
Now, we are given n = 20.
a) Assumptions
- There are 20 independent trials.
- Each trial have two possible outcome: security loose value or security does not lose value.
- The probability for success of each trial is same, p = 0.7
b) P(all 20 securities lose value)
We have to evaluate:
[tex]P(x = 20)\\= \binom{20}{0}(0.7)^0(1-0.7)^{20}\\= 0.0007[/tex]
0.0007 is the probability that all 20 securities lose value.
c) P(at least 15 of them lose value.)
[tex]P(x \geq 15)\\= P(x=15) + P(x = 16) + P(x=17) + P(x=18) +P(x = 19) +P(x = 20)\\ \binom{20}{15}(0.7)^{15}(1-0.7)^{5} +...+ \binom{20}{20}(0.7)^{20}(1-0.7)^{0} \\=0.4163[/tex]
d) P(less than 5 of them gain value.)
P(gain value) = 1 - 0.7 = 0.3
[tex]P(x < 5)\\= P(x=0) + P(x = 1) + P(x=2) + P(x=3) +P(x = 4)\\ \binom{20}{0}(0.3)^{0}(1-0.3)^{20} +...+ \binom{20}{4}(0.3)^{4}(1-0.3)^{16} \\=0.2375[/tex]
