Hi Kimchi

Significant figures are importantly considered when the numerical quantities are from the measurements. 

Since chemistry is dealing with measurement, the level of precision is dependent on what tool is being used. 

Each equipment will provide different numerical values such as values with one decimal place or two decimal places. 

Because of that different significant figures given by different equipment, the effect will follow during the computation using those quantities.

In mathematics, we consider very ideal world with ideally exact numbers.

Those numbers are exactly given, which means the number of significant figures is infinite.

So, it's a big difference between math and chem. 

Best,

Kelda