a) This question is another probability question. A tree drawn makes life much easier when it comes to solving this question. Refer to slide 3. To find the probability of him having work given that he was late you must:
STEP 1: Find probability of P(WL) and P(NWL)
-just like the other probability question -multiply probability of W and L -multiply probability of NW and L
STEP 2: Find on tree where there was a case that he was late
-case found on two branches -another given that question meaning P(W/L) -plug in values -work shown on slide 4
b) STEP 1: Circle on tree when case is NL
-2 branches circled - not a given that question because only one case needed to be satisfied which is NL
STEP 2: Add probabilities
-can either be P(WNL) or P(NWNL) -keyword or meaning to add -work shown on slide 5