Answer:
You should use 5 digits to the right of the decimal point.
Explanation:
To be precise in the mathematical operation you have to conserve all significant digits
.
Replace the scientific notation for its equivalent in decimal notation:
2.70 x 10-4 g = 0.00027 g
4.21 x 10-3 g = 0.00421 g
Then, compute the addition and subtraction
:
0.01360 g
+
0.00027 g
-
0.00421 g
-------------
0.00966 g = 9.66 x 10-3 g
That means you should use 5 digits to the right of the decimal point, which are the biggest amount of digits necessary to represent 2 of the numbers involved in the mathematical operation.