Question 1201433
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Answers:
a) <font color=red size=4>1/3</font>
b) <font color=red size=4>2/3</font>


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Explanation:


I'll refer to the persons as C and D.
I'll also refer as the restaurants as R1,R2,R3.


Let's say C picks R1.
D has probability <font color=red>1/3</font> of also picking R1.


This logic applies if C chose R2, or R3.
Effectively we can make person C the anchor, and have the question be reframed to "What are the chances person D picked the anchor restaurant?". The order of the restaurants doesn't matter, and neither does the order of who selects first.


Therefore, the chances of them <font color=red>meeting</font> is <font color=red>1/3</font>


The chances of them <font color=red>missing</font> each other is 1 - (1/3) = <font color=red>2/3</font>


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Another approach:


Form a table showing all possible combos
C's choices are along the top
D's choices are along the left side
<table border = "1" cellpadding = "5"><tr><td></td><td>R1</td><td>R2</td><td>R3</td></tr><tr><td>R1</td><td>X</td><td></td><td></td></tr><tr><td>R2</td><td></td><td>X</td><td></td></tr><tr><td>R3</td><td></td><td></td><td>X</td></tr></table>
The X's refer to instances where they meet. Otherwise, they miss each other.


There are 3*3 = 9 outcomes total


There are 3 X's out of 9 slots total.
3/9 = <font color=red>1/3</font> = chances of them <font color=red>meeting</font>
6/9 = <font color=red>2/3</font> = chances of them <font color=red>missing </font> each other.


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Edit:


Another approach:


Using inspiration from the tutor @ikleyn, we can have the following
X = P(C picks R1, D picks R1) = P(C picks R1)*P(D picks R1) = (1/3)*(1/3) = 1/9
Y = P(C picks R2, D picks R2) = P(C picks R2)*P(D picks R2) = (1/3)*(1/3) = 1/9
Z = P(C picks R3, D picks R3) = P(C picks R3)*P(D picks R3) = (1/3)*(1/3) = 1/9


Then X+Y+Z = (1/9)+(1/9)+(1/9) = 3/9 = <font color=red>1/3</font> represents the chances of them meeting, and <font color=red>2/3</font> is the chance of them not meeting.
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