
Let

, so that

and

. The integral is then equivalent to
Answer:
(a) 0.28347
(b) 0.36909
(c) 0.0039
(d) 0.9806
Step-by-step explanation:
Given information:
n=12
p = 20% = 0.2
q = 1-p = 1-0.2 = 0.8
Binomial formula:

(a) Exactly two will be drunken drivers.



Therefore, the probability that exactly two will be drunken drivers is 0.28347.
(b)Three or four will be drunken drivers.


Using binomial we get



Therefore, the probability that three or four will be drunken drivers is 0.3691.
(c)
At least 7 will be drunken drivers.

![P(x\leq 7)=1-[P(x=0)+P(x=1)+P(x=2)+P(x=3)+P(x=4)+P(x=5)+P(x=6)]](https://tex.z-dn.net/?f=P%28x%5Cleq%207%29%3D1-%5BP%28x%3D0%29%2BP%28x%3D1%29%2BP%28x%3D2%29%2BP%28x%3D3%29%2BP%28x%3D4%29%2BP%28x%3D5%29%2BP%28x%3D6%29%5D)
![P(x\leq 7)=1-[0.06872+0.20616+0.28347+0.23622+0.13288+0.05315+0.0155]](https://tex.z-dn.net/?f=P%28x%5Cleq%207%29%3D1-%5B0.06872%2B0.20616%2B0.28347%2B0.23622%2B0.13288%2B0.05315%2B0.0155%5D)
![P(x\leq 7)=1-[0.9961]](https://tex.z-dn.net/?f=P%28x%5Cleq%207%29%3D1-%5B0.9961%5D)

Therefore, the probability of at least 7 will be drunken drivers is 0.0039.
(d) At most 5 will be drunken drivers.



Therefore, the probability of at most 5 will be drunken drivers is 0.9806.
You add 1/4 each year:
800 to 1000 in one year
1000 to 1250 in 2
1250 to around 1812.5