Answer:
a) 20.95% probability of a household having 2 or 5 children.
b) 7.29% probability of a household having 3 or fewer children.
c) 19.37% probability of a household having 8 or more children.
d) 19.37% probability of a household having fewer than 5 children.
e) 92.71% probability of a household having more than 3 children.
Step-by-step explanation:
Binomial probability distribution
The binomial probability is the probability of exactly x successes on n repeated trials, and X can only have two outcomes.
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
In which
is the number of different combinations of x objects from a set of n elements, given by the following formula.
![C_{n,x} = \frac{n!}{x!(n-x)!}](https://tex.z-dn.net/?f=C_%7Bn%2Cx%7D%20%3D%20%5Cfrac%7Bn%21%7D%7Bx%21%28n-x%29%21%7D)
And p is the probability of X happening.
In this problem, we have that:
![n = 12, p = 0.5](https://tex.z-dn.net/?f=n%20%3D%2012%2C%20p%20%3D%200.5)
(a) 2 or 5 children
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
![P(X = 2) = C_{12,2}.(0.5)^{2}.(0.5)^{10} = 0.0161](https://tex.z-dn.net/?f=P%28X%20%3D%202%29%20%3D%20C_%7B12%2C2%7D.%280.5%29%5E%7B2%7D.%280.5%29%5E%7B10%7D%20%3D%200.0161)
![P(X = 5) = C_{12,5}.(0.5)^{5}.(0.5)^{7} = 0.1934](https://tex.z-dn.net/?f=P%28X%20%3D%205%29%20%3D%20C_%7B12%2C5%7D.%280.5%29%5E%7B5%7D.%280.5%29%5E%7B7%7D%20%3D%200.1934)
![p = P(X = 2) + P(X = 5) = 0.0161 + 0.1934 = 0.2095](https://tex.z-dn.net/?f=p%20%3D%20P%28X%20%3D%202%29%20%2B%20P%28X%20%3D%205%29%20%3D%200.0161%20%2B%200.1934%20%3D%200.2095)
20.95% probability of a household having 2 or 5 children.
(b) 3 or fewer children
![P(X \leq 3) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3)](https://tex.z-dn.net/?f=P%28X%20%5Cleq%203%29%20%3D%20P%28X%20%3D%200%29%20%2B%20P%28X%20%3D%201%29%20%2B%20P%28X%20%3D%202%29%20%2B%20P%28X%20%3D%203%29)
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
![P(X = 0) = C_{12,0}.(0.5)^{0}.(0.5)^{12} = 0.0002](https://tex.z-dn.net/?f=P%28X%20%3D%200%29%20%3D%20C_%7B12%2C0%7D.%280.5%29%5E%7B0%7D.%280.5%29%5E%7B12%7D%20%3D%200.0002)
![P(X = 1) = C_{12,1}.(0.5)^{1}.(0.5)^{11} = 0.0029](https://tex.z-dn.net/?f=P%28X%20%3D%201%29%20%3D%20C_%7B12%2C1%7D.%280.5%29%5E%7B1%7D.%280.5%29%5E%7B11%7D%20%3D%200.0029)
![P(X = 2) = C_{12,2}.(0.5)^{2}.(0.5)^{10} = 0.0161](https://tex.z-dn.net/?f=P%28X%20%3D%202%29%20%3D%20C_%7B12%2C2%7D.%280.5%29%5E%7B2%7D.%280.5%29%5E%7B10%7D%20%3D%200.0161)
![P(X = 3) = C_{12,3}.(0.5)^{3}.(0.5)^{9} = 0.0537](https://tex.z-dn.net/?f=P%28X%20%3D%203%29%20%3D%20C_%7B12%2C3%7D.%280.5%29%5E%7B3%7D.%280.5%29%5E%7B9%7D%20%3D%200.0537)
![P(X \leq 3) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) = 0.0002 + 0.0029 + 0.0161 + 0.0537 = 0.0729](https://tex.z-dn.net/?f=P%28X%20%5Cleq%203%29%20%3D%20P%28X%20%3D%200%29%20%2B%20P%28X%20%3D%201%29%20%2B%20P%28X%20%3D%202%29%20%2B%20P%28X%20%3D%203%29%20%3D%200.0002%20%2B%200.0029%20%2B%200.0161%20%2B%200.0537%20%3D%200.0729)
7.29% probability of a household having 3 or fewer children.
(c) 8 or more children
![P(X \geq 8) = P(X = 8) + P(X = 9) + P(X = 10) + P(X = 11) + P(X = 12)](https://tex.z-dn.net/?f=P%28X%20%5Cgeq%208%29%20%3D%20P%28X%20%3D%208%29%20%2B%20P%28X%20%3D%209%29%20%2B%20P%28X%20%3D%2010%29%20%2B%20P%28X%20%3D%2011%29%20%2B%20P%28X%20%3D%2012%29)
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
![P(X = 8) = C_{12,8}.(0.5)^{8}.(0.5)^{4} = 0.1208](https://tex.z-dn.net/?f=P%28X%20%3D%208%29%20%3D%20C_%7B12%2C8%7D.%280.5%29%5E%7B8%7D.%280.5%29%5E%7B4%7D%20%3D%200.1208)
![P(X = 9) = C_{12,9}.(0.5)^{9}.(0.5)^{3} = 0.0537](https://tex.z-dn.net/?f=P%28X%20%3D%209%29%20%3D%20C_%7B12%2C9%7D.%280.5%29%5E%7B9%7D.%280.5%29%5E%7B3%7D%20%3D%200.0537)
![P(X = 10) = C_{12,10}.(0.5)^{10}.(0.5)^{2} = 0.0161](https://tex.z-dn.net/?f=P%28X%20%3D%2010%29%20%3D%20C_%7B12%2C10%7D.%280.5%29%5E%7B10%7D.%280.5%29%5E%7B2%7D%20%3D%200.0161)
![P(X = 11) = C_{12,11}.(0.5)^{11}.(0.5)^{1} = 0.0029](https://tex.z-dn.net/?f=P%28X%20%3D%2011%29%20%3D%20C_%7B12%2C11%7D.%280.5%29%5E%7B11%7D.%280.5%29%5E%7B1%7D%20%3D%200.0029)
![P(X = 12) = C_{12,12}.(0.5)^{12}.(0.5)^{0} = 0.0002](https://tex.z-dn.net/?f=P%28X%20%3D%2012%29%20%3D%20C_%7B12%2C12%7D.%280.5%29%5E%7B12%7D.%280.5%29%5E%7B0%7D%20%3D%200.0002)
![P(X \geq 8) = P(X = 8) + P(X = 9) + P(X = 10) + P(X = 11) + P(X = 12) = 0.1208 + 0.0537 + 0.0161 + 0.0029 + 0.0002 = 0.1937](https://tex.z-dn.net/?f=P%28X%20%5Cgeq%208%29%20%3D%20P%28X%20%3D%208%29%20%2B%20P%28X%20%3D%209%29%20%2B%20P%28X%20%3D%2010%29%20%2B%20P%28X%20%3D%2011%29%20%2B%20P%28X%20%3D%2012%29%20%3D%200.1208%20%2B%200.0537%20%2B%200.0161%20%2B%200.0029%20%2B%200.0002%20%3D%200.1937)
19.37% probability of a household having 8 or more children.
(d) fewer than 5 children
![P(X < 5) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4)](https://tex.z-dn.net/?f=P%28X%20%3C%205%29%20%3D%20P%28X%20%3D%200%29%20%2B%20P%28X%20%3D%201%29%20%2B%20P%28X%20%3D%202%29%20%2B%20P%28X%20%3D%203%29%20%2B%20P%28X%20%3D%204%29)
![P(X = x) = C_{n,x}.p^{x}.(1-p)^{n-x}](https://tex.z-dn.net/?f=P%28X%20%3D%20x%29%20%3D%20C_%7Bn%2Cx%7D.p%5E%7Bx%7D.%281-p%29%5E%7Bn-x%7D)
![P(X = 0) = C_{12,0}.(0.5)^{0}.(0.5)^{12} = 0.0002](https://tex.z-dn.net/?f=P%28X%20%3D%200%29%20%3D%20C_%7B12%2C0%7D.%280.5%29%5E%7B0%7D.%280.5%29%5E%7B12%7D%20%3D%200.0002)
![P(X = 1) = C_{12,1}.(0.5)^{1}.(0.5)^{11} = 0.0029](https://tex.z-dn.net/?f=P%28X%20%3D%201%29%20%3D%20C_%7B12%2C1%7D.%280.5%29%5E%7B1%7D.%280.5%29%5E%7B11%7D%20%3D%200.0029)
![P(X = 2) = C_{12,2}.(0.5)^{2}.(0.5)^{10} = 0.0161](https://tex.z-dn.net/?f=P%28X%20%3D%202%29%20%3D%20C_%7B12%2C2%7D.%280.5%29%5E%7B2%7D.%280.5%29%5E%7B10%7D%20%3D%200.0161)
![P(X = 3) = C_{12,3}.(0.5)^{3}.(0.5)^{9} = 0.0537](https://tex.z-dn.net/?f=P%28X%20%3D%203%29%20%3D%20C_%7B12%2C3%7D.%280.5%29%5E%7B3%7D.%280.5%29%5E%7B9%7D%20%3D%200.0537)
![P(X = 4) = C_{12,4}.(0.5)^{4}.(0.5)^{8} = 0.1208](https://tex.z-dn.net/?f=P%28X%20%3D%204%29%20%3D%20C_%7B12%2C4%7D.%280.5%29%5E%7B4%7D.%280.5%29%5E%7B8%7D%20%3D%200.1208)
![P(X < 5) = P(X = 0) + P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) = 0.0002 + 0.0029 + 0.0161 + 0.0537 + 0.1208 = 0.1937](https://tex.z-dn.net/?f=P%28X%20%3C%205%29%20%3D%20P%28X%20%3D%200%29%20%2B%20P%28X%20%3D%201%29%20%2B%20P%28X%20%3D%202%29%20%2B%20P%28X%20%3D%203%29%20%2B%20P%28X%20%3D%204%29%20%3D%200.0002%20%2B%200.0029%20%2B%200.0161%20%2B%200.0537%20%2B%200.1208%20%3D%200.1937)
19.37% probability of a household having fewer than 5 children.
(e) more than 3 children
Either a household has 3 or fewer children, or it has more than 3. The sum of these probabilities is 100%.
From b)
7.29% probability of a household having 3 or fewer children.
p + 7.29 = 100
p = 92.71
92.71% probability of a household having more than 3 children.