10000 would be correct because 20 only has 1 significant digit. One way to determine the number of significant digits is to write the numbers using scientific notation. You’d have 12000 is 1.2 x 10e4 and 20 is 2 x 10e1. Use the smallest number of significant digits (which would be one in this case).

what if you are adding non-decimal numbers, like 12000 + 20? Is this 12020 or 10000? Thanks!

10000 would be correct because 20 only has 1 significant digit. One way to determine the number of significant digits is to write the numbers using scientific notation. You’d have 12000 is 1.2 x 10e4 and 20 is 2 x 10e1. Use the smallest number of significant digits (which would be one in this case).

no that would be incorrect the answer should be rounded to the thousands place! So it should be 12,000. Because the least precise number is 12,000