Question 1191857
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The ratio of calcium to sulfur is 5:4
The ratio of calcium to oxygen is 5:8


We can flip the second ratio to get
ratio of oxygen to calcium is 8:5


Then join up the 8:5 ratio with the 5:4 ratio to get the triple ratio 8:5:4
This describes the ratio of oxygen to calcium to sulfur in that exact order.


Scale up that triple ratio by x to get 8x:5x:4x
The parts add to 8x+5x+4x = 13x+4x = 17x


Set this equal to the total amount of calcium sulfate (*[tex \large CaSO_4]) we have, which is 34 grams.
17x = 34
x = 34/17
x = 2


Therefore, the ratio 8x:5x:4x is 8*2:5*2:4*2 or 16:10:8


Telling us that there are...
<font color=red>16 grams of oxygen</font>
<font color=red>10 grams of calcium</font>
<font color=red>8 grams of sulfur</font>
Each describes the mass value, and not weight. 
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