Question 1162255
<br>
Given that he walks to school on Tuesday, there are only four possible scenarios.  Calculate the probability of each one.<br>
{{{P(W,W,W) = (3/5)(3/5) = 9/25}}}<br>
{{{P(W,W,B) = (3/5)(2/5) = 6/25}}}<br>
{{{P(W,B,W) = (2/5)(3/10) = 6/50 = 3/25}}}
{{{P(W,B,B) = (2/5)(7/10) = 14/50 = 7/25}}}<br>
Note you don't need to find all those probabilities to answer the questions that are asked.  But since the number of cases is small, finding all of them and seeing that the sum of all the probabilities is 1 gives you some confidence that you are working the problem correctly.<br>
1) If he walks to school on Tuesday, then the probability that he goes by bus on Thursday is {{{P(W,W,B) + P(W,B,B) = 6/25+7/25 = 13/25}}}.<br>
2) If he walks to school on both Tuesday and Thursday, then the probability that he also walks to school on Wednesday is {{{P(W,W,W) = 9/25}}}.<br>