## ← Robot Sensing 4 - Intro to Statistics

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Showing Revision 4 created 05/25/2016 by Udacity Robot.

1. I will now make your life really hard.
2. Suppose there are 3 places in the world, not just 2.
3. There are a red one and 2 green ones.
4. And for simplicity, we'll call them A, B, and C.
5. Let's assume that all of them
6. have the same prior probability of 1/3 or 0.333, so on.
7. Let's say the robot sees red,
8. and as before, the probability of seeing red
9. in Cell A is 0.9.
10. The probability of seeing green in Cell B
11. 0.9.
12. Probability of seeing green in Cell C
13. is also 0.9.
14. So what I've changed is,
15. I've given the hidden variable,
16. kind of like the cancer/non cancer variable,
17. 3 states.
18. There's not just 2 as before, A or B.
19. It's now A, B, or C.
20. Let's solve this problem together,
21. because it follows exactly the same recipe as before,
22. even though it might not be obvious.
23. So let me ask you,
24. what is the joint of being in Cell A
25. after having seen the red color?
26. This is the joint as before.