Adding and subtracting Time | Navigation Problem

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Adding Times
Follow these steps:

Add the hours
Add the minutes
If the minutes are 60 or more, subtract 60 from the minutes and add 1 to hours
Like this:

Easy example: What is 2:45 + 1:10 ?
Add the Hours: 2+1 = 3
Add the Minutes: 45+10 = 55
The minutes are OK, so the answer is 3:55

Hard example: What is 2:45 + 1:20 ?
Add the Hours: 2+1 = 3
Add the Minutes: 45+20 = 65
The minutes are 60 or more, so

subtract 60 from minutes (65−60 = 5 Minutes)
and add 1 to Hours (3+1 = 4 Hours)
The answer is 4:05

Subtracting Times
Follow these steps:

Subtract the hours
Subtract the minutes
If the minutes are negative, add 60 to the minutes and subtract 1 from hours.
Like this:

Easy example: What is 4:10 - 1:05 ?
Subtract the Hours: 4−1 = 3
Subtract the Minutes: 10−5 = 5
The minutes are OK, so the answer is 3:05

Hard example: What is 4:10 - 1:35 ?
Subtract the Hours: 4−1 = 3
Subtract the Minutes: 10−35 = −25
The minutes are less than 0, so:

add 60 to Minutes (−25+60 = 60−25 = 35 Minutes)
and subtract 1 from Hours (3−1 = 2 Hours)
The answer is 2:35

(Note: did you see how we changed "−25+60" to "60−25" ... that is perfectly fine and makes the calculation easier.)