In cotrimoxazole, sulphamethoxazole and trimethoprim are in the ratio of-

Ans. is 'c' i.e., 5 : 1 o Optimal synergy in case of most organism is exhibited at a concentration ratio of Sulphamethoxazole 20: Trimethoprim 1 (This ratio is obtained in plasma when two are given in a dose ratio of 5:1).