Which quantity expresses the sum (2.1 g + 33.566 g + 12.22 g) to the proper degree of precision

First let us get the sum of the numbers.

2.1 g + 33.566 g + 12.22 g = 47.886 g

Now to get the proper degree of precision, the amount of decimal places should be equal to the least decimal places of the numbers that were added. In this case, 2.1 g has the least number of decimal places which is equal to 1, hence the correct answer is:

47.9 g