2.2) Rounding and significant digits. 

A. Below is a dataset of whole rock analyses obtained by XRF and the precision on each of the elements. 
Determine the correct number of digits for each data point. 

Sample		SiO2   	Al2O3   	CaO   	MgO   	Na2O   
433-1			60.0531	2.1214	7.5634	0.943	4	0.03213
435-1			60.3245	7.5239	3.5426	1.211	3	0.00435
436-1			70.1214	4.9095	0.0213	0.00214	0.67834
438-2			38.3452	0.0231	0.5346	30.1231	0.02312
439-1			8.4535	0.2342	40.2134	10.2434	0.43567
439-4			50.4536	18.235	0.2123	8.34241	8.45356
440-1			55.7789	9.5467	0.8767	1.34259	3.23453

precision 		1.2%		4%		8%		7%		12%

You are using the data to calculate a geochemical indicator with the formula:

	GCI = (SiO2 + 0.5 * Na2O) / (CaO + 0.5 * Al2O3) 

B. Determine the propagated error equation for this formula.
C. Calculate the GCI and its uncertainty for each sample and determine the correct number of significant
digits for the result.