【Question 15】
In the plane, there are 50 lines, of which 20 are mutually parallel. These 50 lines can divide the plane into a maximum of $\qquad$ parts.
【Analysis and Solution】
30 lines can divide the plane into at most $2+2+3+\cdots+30=466$ parts; after that, each additional line can intersect with the previous 30 lines at most 30 times, these 30 intersection points can divide the newly added line into $30+1=31$ segments; each segment will add 1 part to the original plane, so 31 segments will add 31 parts; the plane can be divided into at most $466+31 \times 20=1086$ parts.