Tok Aba has a factory producing chocolates located at the upper stream of Bamboo River. At the lower stream of the river, Adudu owns a freshwater fish farm. Tok Aba's chocolate factory pollutes the river and affects Adudu's fish production. It is a choice for Tok Aba whether to install a filter and for Adudu whether to install a treatment plant. Table 1 shows the profit of Tok Aba and Adudu in different situations.

Jadual 1: Keuntungan Tok Aba dan Adudu Table 1: Profit of Tok Aba and Adudu Situasi / Situation Tok Aba (RM) Adudu (RM) Tiada penapis atau perawat air / 10,000 2,000 No filter or treatment plant Ada penapis; tiada perawat air / 6,000 10,000 Filter, no treatment plant Tiada penapis; ada perawat air / 10,000 4,000 No filter; treatment plant Ada penapis; ada perawat air / 6,000 6,000 Filter; treatment plant