There are 3 significant figures in the number 0.00666. They are each of the non-zero number 6's. The zero's before a number are not significant. The zeroes AFTER a number ARE significant.
For example:
0.006660 has four significant figures because there is a zero after nonzeroes.
0.00666 only has three significant figures because the zeros before a significant figure are not significant.
Any Questions?
