Answer:
0.0939 = 9.39% probability that there will be exactly 4 sets of twins.
Step-by-step explanation:
For each birth, there is only two possible outcomes. Either it results in twins, or it does not. The probability of a birth resulting in twins is independent of any other birth. This means that the binomial probability distribution is used to solve this question.
Binomial probability distribution
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.
[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]
In which [tex]C_{n,x}[/tex] is the number of different combinations of x objects from a set of n elements, given by the following formula.
[tex]C_{n,x} = \frac{n!}{x!(n-x)!}[/tex]
And p is the probability of X happening.
The probability that a birth will result in twins is 0.017.
This means that [tex]p = 0.017[/tex]
120 births:
This means that [tex]n = 120[/tex]
The probability that there will be exactly 4 sets of twins is?
This is P(X = 4).
[tex]P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}[/tex]
[tex]P(X = 4) = C_{120,4}.(0.017)^{4}.(0.983)^{116} = 0.0939[/tex]
0.0939 = 9.39% probability that there will be exactly 4 sets of twins.
