This can be done using areas. The probability is calculated as the ratio of two areas.
All points with x-coordinate from 0 to 8 and y-coordinate from 0 to 4 form a simple shape (rectangle). Its lower-left corner is positioned at the origin. Draw it on a graph.
Within this rectangular region, all of the points lying below the line x+y=4 also form a simple shape (triangle). To see it, plot the line through the rectangle on your graph.
Calculate the area of the rectangular region.
Calculate the area of the triangular region.
The probability is the ratio of the smaller region to the larger.
Questions? :cool: