Question 371615
There are two sets of 2 days in the week that begin with the same letter. Let's say that they all chose a day beginning with S. For a single person the probability of choosing Saturday is 1/2.
It doesn't make any difference what the 1st one chooses. The others have to chose the same day as the 1st.
1/2 * 1/2 = 1/4  the probability that all three select the same day, given that all three select a day beginning with the same letter. 
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Ed