Hydrogen and oxygen combine to form H₂O₂ and H₂O containing 5.93% and  11.2%  hydrogen respectively The data illustrates ;

In H₂O₂ :

Mass ratio of H and O = 5.93 : 94.07

mass of Oxygen combining with 1 gm (fixed) of H = $\frac{94.07}{5.93}$ = 15.86 gm 

In H₂O : 

Mass ratio of H and O = 11.2 : 88.8

mass of oxygen combining with 1 gm (fixed) of H = $\frac{88.8}{11.2}$ = 7.92

Ratio of Oxygen combining with fixed mass of Hydrogen = $\frac{15.86}{7.92} : \frac{7.92}{7.92}$ = 2 : 1

This explains law of multiple proportions