Final answer:
To compare 394,602 and 389,440, the ten-thousands place is used. Since '9' is greater than '8', it is concluded that 394,602 is greater than 389,440.
Step-by-step explanation:
The student has asked where to perform a comparison between two numbers: 394,602 and 389,440.
Comparing large numbers involves looking at each place value, starting from the left (the highest place value) and moving to the right. Both numbers should be treated as whole numbers since there are no decimal places.
First, compare the digits in the hundred-thousands place. Since both numbers have a '3' in that place, you compare the next place value, the ten-thousands. In 394,602, there is a '9', and in 389,440, there is an '8'. As '9' is greater than '8', we conclude that 394,602 is greater than 389,440 without needing to compare the subsequent digits.
In summary, the place value used to compare these two numbers is the ten-thousands place.