Significant figures are important in reporting values especially in mathematics and chemistry. This is for the purposes of consistency and precision. When doing calculations, we sometimes round off numbers which affects the quality of our measurements. As a convention, significant figures are to be followed. There are three rules for significant figures.
1. All nonzero numbers are significant.
2. All zeros between nonzero numbers are significant.
3. All zeros after the decimal point are significant.
Following the rules, I think all of the numbers in 34.20 are significant. Thus, there are a total of 4 significant figures.
