Answer:
look at the digit after the first non-zero digit if rounding to two significant figures. draw a vertical line after the place value digit that is required. if it's 5 or more, increase the previous digit by one. if it's 4 or less, keep the previous digit the same.
The second significant figure of a number is the digit after the first significant figure. This is true even if the digit is zero. Hence the second significant figure of 20,499 is 0, as is the second significant figure of 0.0020499.