express the sum of 9.78 g and 7.0 g using the correct number of significant digits.
a. 10 g
b. 16.78 g
c. 16.8 g
d. 17 g

The correct answer is 16.8 g (option C)

Explanation:

Step 1: Data given

9.78 grams + 7.0 grams

Rule significant numbers say:

⇒ Non-zero digits are always significant.

⇒ Any zeros between two significant digits are significant.

⇒ A final zero or trailing zeros in the decimal portion ONLY are significant.

For addition and subtraction, look at the places to the decimal point.  Add or subtract in the normal way, then round the answer to the LEAST number of places to the decimal point of any number in the problem.

9.78 g+ 7.0 g = 16.78 grams

Significant numbers = 1 decimal

16.78 ⇒ 16.8

The correct answer is 16.8 g (option C)

the answer is either b or c