Step 1: Find the 3rd decimal place:
The 3rd decimal place in 108.1239 is 3
Step 2: Look at the decider digit
This is the next digit
The 4th decimal place in 108.1239 is 9
Step 3: Evalute the decider digit (9):
Since 9 >= 5, then we round the 3rd decimal place of 3 from Step 1 up one to 4
3 + 1 = 4
Step 4: Answer:
108.124
