# How many significant figures are in the measurement 0.0105 km?

Aug 17, 2016

$3$

#### Explanation:

The first and most important thing to notice here is that your measurement contains two non-zero digits, $1$ and $5$.

As you know, all non-zero digits are significant, so right from the start you know that your measurement contains at least two significant figures

$0.0 \textcolor{p u r p \le}{1} 0 \textcolor{p u r p \le}{5} \to$ two non-zero digits

Now, the zero that precedes the decimal point is not significant because it acts as a placeholder zero for a number that is smaller than $1$.

The same can be said for the zero that follows the decimal point. Once again, this zero is not significant because the number is smaller than $1$.

Finally, the zero that follows $1$ and precedes $5$ is a sandwiched zero, which basically means that it is being flanked by two non-zero digits.

All sandwiched zeroes are significant, which means that your measurement has a total of three significant figures, two non-zero digits and a sandwiched zero.

$\textcolor{red}{0} . \textcolor{red}{0} \textcolor{p u r p \le}{1} \textcolor{\mathrm{da} r k g r e e n}{0} \textcolor{p u r p \le}{5} \to$ three sig figs