Answer:
Step-by-step explanation:
From the information given:
the rate of the cars = ![\dfrac{1}{5} \ car / min = 0.2 \ car /min](https://tex.z-dn.net/?f=%5Cdfrac%7B1%7D%7B5%7D%20%5C%20car%20%2F%20min%20%3D%200.2%20%5C%20car%20%2Fmin)
the rate of the buses = ![\dfrac{1}{10} \ bus / min = 0.1 \ bus /min](https://tex.z-dn.net/?f=%5Cdfrac%7B1%7D%7B10%7D%20%5C%20bus%20%2F%20min%20%3D%200.1%20%5C%20bus%20%2Fmin)
the rate of motorcycle = ![\dfrac{1}{30} \ motorcycle / min = 0.0333 \ motorcycle /min](https://tex.z-dn.net/?f=%5Cdfrac%7B1%7D%7B30%7D%20%5C%20motorcycle%20%2F%20min%20%3D%200.0333%20%5C%20motorcycle%20%2Fmin)
The probability of any event at a given time t can be expressed as:
![P(event \ (x) \ in \ time \ (t)\ min) = \dfrac{e^{-rate \times t}\times (rate \times t)^x}{x!}](https://tex.z-dn.net/?f=P%28event%20%20%5C%20%28x%29%20%5C%20%20in%20%20%5C%20time%20%5C%20%20%28t%29%5C%20min%29%20%3D%20%5Cdfrac%7Be%5E%7B-rate%20%5Ctimes%20t%7D%5Ctimes%20%28rate%20%5Ctimes%20t%29%5Ex%7D%7Bx%21%7D)
∴
(a)
![P(2 \ car \ in \ 20 \ min) = \dfrac{e^{-0.20\times 20}\times (0.2 \times 20)^2}{2!}](https://tex.z-dn.net/?f=P%282%20%5C%20car%20%5C%20%20in%20%20%5C%2020%20%5C%20%20min%29%20%3D%20%5Cdfrac%7Be%5E%7B-0.20%5Ctimes%2020%7D%5Ctimes%20%280.2%20%5Ctimes%2020%29%5E2%7D%7B2%21%7D)
![P(2 \ car \ in \ 20 \ min) =0.1465](https://tex.z-dn.net/?f=P%282%20%5C%20car%20%5C%20%20in%20%20%5C%2020%20%5C%20%20min%29%20%3D0.1465)
![P ( 1 \ motorcycle \ in \ 20 \ min) = \dfrac{e^{-0.0333\times 20}\times (0.0333 \times 20)^1}{1!}](https://tex.z-dn.net/?f=P%20%28%201%20%5C%20motorcycle%20%5C%20in%20%5C%2020%20%5C%20min%29%20%3D%20%5Cdfrac%7Be%5E%7B-0.0333%5Ctimes%2020%7D%5Ctimes%20%280.0333%20%5Ctimes%2020%29%5E1%7D%7B1%21%7D)
![P ( 1 \ motorcycle \ in \ 20 \ min) = 0.3422](https://tex.z-dn.net/?f=P%20%28%201%20%5C%20motorcycle%20%5C%20in%20%5C%2020%20%5C%20min%29%20%3D%200.3422)
![P ( 0 \ buses \ in \ 20 \ min) = \dfrac{e^{-0.1\times 20}\times (0.1 \times 20)^0}{0!}](https://tex.z-dn.net/?f=P%20%28%200%20%5C%20buses%20%20%5C%20in%20%5C%2020%20%5C%20min%29%20%3D%20%5Cdfrac%7Be%5E%7B-0.1%5Ctimes%2020%7D%5Ctimes%20%280.1%20%5Ctimes%2020%29%5E0%7D%7B0%21%7D)
![P ( 0 \ buses \ in \ 20 \ min) = 0.1353](https://tex.z-dn.net/?f=P%20%28%200%20%5C%20buses%20%20%5C%20in%20%5C%2020%20%5C%20min%29%20%3D%20%200.1353)
Thus;
P(exactly 2 cars, 1 motorcycle in 20 minutes) = 0.1465 × 0.3422 × 0.1353
P(exactly 2 cars, 1 motorcycle in 20 minutes) = 0.0068
(b)
the rate of the total vehicles = 0.2 + 0.1 + 0.0333 = 0.3333
the rate of vehicles with exact change = rate of total vehicles × P(exact change)
![= 0.3333 \times \dfrac{1}{4}](https://tex.z-dn.net/?f=%3D%200.3333%20%5Ctimes%20%5Cdfrac%7B1%7D%7B4%7D)
= 0.0833
∴
![P(zero \ exact \ change \ in \ 10 minutes) = \dfrac{e^{-0.0833\times 10}\times (0.0833 \times 10)^0}{0!}](https://tex.z-dn.net/?f=P%28zero%20%5C%20exact%20%5C%20change%20%5C%20in%20%5C%2010%20minutes%29%20%3D%20%5Cdfrac%7Be%5E%7B-0.0833%5Ctimes%2010%7D%5Ctimes%20%280.0833%20%5Ctimes%2010%29%5E0%7D%7B0%21%7D)
P(zero exact change in 10 minutes) = 0.4347
c)
The probability of the 7th motorcycle after the arrival of the third motorcycle is:
![P( 4 \ motorcyles \ in \ 45 \ minutes) =\dfrac{e^{-0.0333\times 45}\times (0.0333 \times 45)^4}{4!}](https://tex.z-dn.net/?f=P%28%204%20%20%5C%20motorcyles%20%5C%20%20in%20%20%5C%2045%20%20%5C%20minutes%29%20%3D%5Cdfrac%7Be%5E%7B-0.0333%5Ctimes%2045%7D%5Ctimes%20%280.0333%20%5Ctimes%2045%29%5E4%7D%7B4%21%7D)
![P( 4 \ motorcyles \ in \ 45 \ minutes) =0.0469](https://tex.z-dn.net/?f=P%28%204%20%20%5C%20motorcyles%20%5C%20%20in%20%20%5C%2045%20%20%5C%20minutes%29%20%3D0.0469)
Thus; the probability of the 7th motorcycle after the arrival of the third one is = 0.0469
d)
P(at least one other vehicle arrives between 3rd and 4th car arrival)
= 1 - P(no other vehicle arrives between 3rd and 4th car arrival)
The 3rd car arrives at 15 minutes
The 4th car arrives at 20 minutes
The interval between the two = 5 minutes
<u>For Bus:</u>
P(no other vehicle other vehicle arrives within 5 minutes is)
= ![\dfrac{6}{12} = 0.5](https://tex.z-dn.net/?f=%5Cdfrac%7B6%7D%7B12%7D%20%3D%200.5)
<u>For motorcycle:</u>
![= \dfrac{2 }{12} = \dfrac{1 }{6}](https://tex.z-dn.net/?f=%3D%20%5Cdfrac%7B2%20%7D%7B12%7D%20%20%3D%20%5Cdfrac%7B1%20%7D%7B6%7D)
∴
The required probability = ![1 - \Bigg ( \dfrac{e^{-0.5 \times 0.5^0}}{0!} \times \dfrac{e^{-1/6}\times (1/6)^0}{0!} \Bigg)](https://tex.z-dn.net/?f=1%20-%20%5CBigg%20%28%20%5Cdfrac%7Be%5E%7B-0.5%20%5Ctimes%200.5%5E0%7D%7D%7B0%21%7D%20%5Ctimes%20%5Cdfrac%7Be%5E%7B-1%2F6%7D%5Ctimes%20%281%2F6%29%5E0%7D%7B0%21%7D%20%20%5CBigg%29)
= 1- 0.5134
= 0.4866