Answer:
-3
Step-by-step explanation:


I got 36000000 . Hope this helps
Answer:
The expected number of days until prisoner reaches freedom is 12 days
Step-by-step explanation:
From the given information:
Let X be the random variable that denotes the number of days until the prisoner reaches freedom.
We can evaluate E(X) by calculating the doors selected, If Y be the event that the prisoner selects a door, Then;
E(X) = E( E[X|Y] )
E(X) = E [X|Y =1 ] P{Y =1} + E [X|Y =2 ] P{Y =2} + E [X|Y =3 ] P{Y =3}
![E(X) = (2 + E[X])\dfrac{1}{2}+ (4 + E[X])\dfrac{3}{10}+ 1 (\dfrac{2}{10})](https://tex.z-dn.net/?f=E%28X%29%20%3D%20%282%20%2B%20E%5BX%5D%29%5Cdfrac%7B1%7D%7B2%7D%2B%20%284%20%2B%20E%5BX%5D%29%5Cdfrac%7B3%7D%7B10%7D%2B%201%20%28%5Cdfrac%7B2%7D%7B10%7D%29)
![E(X) = (2 + E[X])0.5+ (4 + E[X])0.3+ 0.2](https://tex.z-dn.net/?f=E%28X%29%20%3D%20%282%20%2B%20E%5BX%5D%290.5%2B%20%284%20%2B%20E%5BX%5D%290.3%2B%200.2)
Solving for E[X]; we get
E[X] = 12