# Question #d6001

Sep 2, 2017

Two.

#### Explanation:

As you know, all non-zero digits are significant, so right from the start, you know that this measurement has at least $2$ significant figures because it contains two non-zero digits.

$0.00078 \text{ "-> " " "two non-zero digits: } 7 , 8$

Now, your goal is to figure out if any of the four zeroes are significant.

In this regard, you can use the fact for numbers that are $< 1$, all zeroes that follow the decimal point are only significant if they also follow a non-zero digit.

If the zeroes follow the decimal point directly, then they are not significant.

$0.00078 < 1$

so you must at the three zeroes that follow the decimal point. Since they do not follow any non-zero digits, you can say that they are not significant.

$\textcolor{b l a c k}{0. \textcolor{red}{000} 78} \text{ " -> " " "three non-significant zeroes}$

Similarly, for numbers that are $< 1$, the zero that precedes the decimal point is known as a placeholder zero and is not significant.

$\textcolor{b l u e}{0} . \textcolor{b l a c k}{00078} \text{ " ->" " "a non-significant placeholder zero}$

Therefore, you can say that your measurement has $2$ significant figures, the non-zero digits.