47000 has 2 significant figures while 47000.000 has 8 significant figures...why? when both are the same value.

 

Significant figures refer to the digits in a measured or calculated value that carry meaningful information about its precision. 

They include all digits known with certainty based on the measuring tool, plus the very first estimated (uncertain) digit i.e. rounded digit. 

Understanding Certainty and Estimation

When measuring, for instance, a table length with a standard centimeter ruler, you might observe that it lands between 15.2 cm and 15.3 cm.

You know for sure it is 15 cm.

You visually estimate the last decimal place, guessing it falls about halfway, reporting 15.25 cm.

In this measurement, 1, 5, and 2 are completely certain, while the 5 is an estimate. All four are your significant figures.