Bronze is an alloy (a mixture of metals) of copper (Cu) and tin (Sn). A sample of brinze is analysed and found to contain 8.0% tin by mass. Therefore, in this sample, the ratio of copper atoms:tin atoms (Cu/Sn) is?© BrainMass Inc. brainmass.com September 25, 2018, 1:46 am ad1c9bdddf - https://brainmass.com/chemistry/stoichiometry/percent-mass-composition-102702
In these types of quesitons, it is best to take 100 grams of your compound..... in this case ...
The solution discusses the percent by mass composition.