If you subtract 23.47 km from 560.589 km, how many significant digits would your answer have?

560.589 - 23.47 is hmm 537.119  < 6 significant digits

alrite... looks good, however, when it comes to dealing with significant digits, for addition/subtraction, we go with the lowest significant amount for decimals, in this case,

560.589  <--- has 6 significant digits, accurate to the 1000th place
23.47     <--- has 4 significant digits, and is accurate to the 100th place

thus, our answer will have to be rounded up in 2 significant decimals, or 537.12
and that only has 5 significant digits, since is rounded up to the 100th place.