Question 1181566
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The responses from the other tutor are correct for parts (a) and (c).<br>
For part (b), the statement of the problem is that we are to find the probability that we "make our sale on the first, second, or third​ call".<br>
That statement is logically nonsense.  The "or" indicates we are talking about a particular call; but the "first, second, or third..." indicates we are talking about one of three calls.<br>
To make sense, part (b) should ask for the probability that the FIRST sale is made on the first, second, or third call.<br>
But since that is not what the problem (as you show it) asks for; we can't know what probability they are really asking for. But it definitely does not mean what the other tutor interpreted it as -- making sales on ALL THREE of the first three calls.<br>