picture inserted
seriously?
the width of the nominal rectangle is 20 units
the height is 15
the nominal rectangle has area of 300 units
we subtract off a right triangle with base and height of 5 units
this triangle has area of 25/2 units
The resulting area is 300- 25/2 = 287.5 units
Divide this by the total area of 300 units and you get
p = 287.5/300 = 0.95833333 i.e. 0.96, choice (e)
Oh. Totally different question.
In general what you're looking at here is the probability that Emily gets to the post office before the mailman collects the letters.
If she gets there before 8:15 it's a sure thing.
But between 8:15 and 8:20 the possibility exists that the mailman gets there first.
As both are on uniform distributions the probability that one arrives earlier than the other is 50/50. Hence the slope of 1 on the bit that's cut off.
That's where the 2 5's come from.