There are two common oxides of sulphur, one of which contains 50% O2 by weight, the other almost exactly 60%. The weights of sulphur which combine with 1 g of O2 (fixed) are in the ratio of

First oxide                    Second oxideSulphur 50%                    40%Oxygen 50%                    60%In first oxide I parts oxygen combines with sulphur =5050=1Similarly for second oxide =4060=0.67So the ratio is 1:0.67 or 3 : 2