#### Answer

3

#### Work Step by Step

Applying the rules on page 162 of the book, we find the number of significant digits (the accuracy) of the measurement 4.06 kg.
We use rule #1: all non-zero digits are significant. Thus "4,6" are significant.
We also use rule #2: all zeros between significant digits are significant; that is, we have here 1 zero, which is significant.
Thus, there are 3 significant digits.