Final answer:
To round 0.01842 km to three significant figures, round the number down since the fourth decimal place is 4, resulting in a rounded number of 0.018 km.
Step-by-step explanation:
To round the number 0.01842 km to three significant figures, we look at the digit in the fourth decimal place. Since the digit is 4, which is less than 5, we will round down. The third significant figure, which is the second decimal place, remains 8. Therefore, the rounded number is 0.018 km.