Question: Taking into account of the significant figures, what is the value of 9.99 m − 0.0099 m? [PMT/NEET-2020]
a. 9.9801 m
b. 9.98 m
c. 9.980 m
d. 9.9 m

Solution:

We need to evaluate

$
9.99\ \text{m} – 0.0099\ \text{m} = 9.9801\ \text{m}
$

Now apply the rule of significant figures for subtraction:

• For addition and subtraction, the reported result must have the same number of decimal places as the term with the fewest decimal places.
• Here:
• $9.99\ \text{m}$ has 2 decimal places.
• $0.0099\ \text{m}$ has 4 decimal places.
• Therefore, the final result must be expressed with 2 decimal places.

$
9.9801 \ \text{m} \approx 9.98 \ \text{m}
$

Answer: b. 9.98 m