Sid and Nancy both need to buy pens for school. The bookstore has only two types of pens:
Basic blue pens (B), which cost $.60 each.
Long-lasting green pens (G), which have twice as much ink as the blue pens, and cost $1.00 each.
Nancy needs the pens to draw multi-colored graphs in her Economics class. For Nancy, these two types of pens are perfect complements. The graphs Nancy must draw require the ink of two basic blue pens for every one long-lasting green pen, and her production function is: q = min(25B,50G). Nancy will need to draw 100 graphs.
Sid needs the pens to write essays in his English class. One essay requires the ink of one basic blue pen or ½ of a long-lasting pen, and ink color is irrelevant. So, for Sid, these two types of pens are perfect substitutes, and his production function is: q = B + 2G. Sid will need to write 10 essays.