假定金含量是90%,则有金的质量＝a*90%克,体积＝a*90%/19.3cm^3;有银a*(1-90%)=a*10%克,体积＝a*10%/10.5cm^3,总体积＝a*90%/19.3＋a*10%/10.5cm^3；
1.若首饰的体积V＞a*90%/19.3＋a*10%/10.5cm^3,说明黄金含量低于90%
2.若首饰的体积V＜a*90%/19.3＋a*10%/10.5cm^3,说明黄金含量高于90% .