[tortoise]

A sample of 6.68 g of calcium combines exactly with 6.33g of fluorine, forming calcium fluoride, CaF₂. Find the relative masses of the atoms of calcium and fluorine. Check your  answer  using  a  table  of  atomic weights.  If  the  formula were not known, could you still do this calculation?

- Which calculations do I have to do? I don't understand the term "relative mass" clearly. Does it the same as "atomic mass"?
- If  the  formula (ie CaF₂?) were not known, we could still do the calculations, because we could find the formula and then continue as above.. right? or do we have another way?

[AWK]

A sample of 6.68 g of calcium combines exactly with 6.33g of fluorine, forming calcium fluoride, CaF2.

From these data you can calculate M_Ca:M_F as 6.68:3.165. As you know, atomic masses of elements very often may be a whole numbers. Multiplying these number in above ratio 2.106:1
in turns by whole numbers you can get (multiplying by 9) 18.95: 1 ~19:9 (these numbers may be accepted as relative masses of both elements. But looking at  the periodic table you can find that a proper multiplier is 19 giving 40:19 (both numbers are in fact atomic masses of Ca and F, respectively)