Math · Ratios & measurement
Time, Temperature, and Applied Measurement
Estimated time includes reading and one quiz. Take the time you need.
Start here: key ideas
- Elapsed time is an interval, not a clock reading.
- 24-hour times after 12:59 subtract 12 hours for p.m. time.
- Celsius and Fahrenheit conversions require both scaling and an offset.
- A measuring tool supports only the precision shown by its divisions.
What you’ll be able to do
- Find elapsed time across an hour or midnight.
- Convert between 12-hour and 24-hour time and between Celsius and Fahrenheit.
- Read a measurement scale to its supported precision.
Elapsed time is an interval, not a clock reading. 24-hour times after 12:59 subtract 12 hours for p.m. time.
Optional review
If you’d like to review the basics, visit Measurement Systems and Unit Conversions. You can start this lesson without completing those first.
Find elapsed and military time
Elapsed time is the distance from start to finish. Worked example 1: From 9:47 a.m. to 12:18 p.m., move 13 minutes to 10:00, 2 hours to noon, and 18 minutes to 12:18. Total: 2 hours 31 minutes. This avoids subtracting minutes that would require borrowing.
In 24-hour time, 0000 is midnight and 1200 is noon. For a p.m. time after noon, add 12 to the hour: 7:25 p.m. becomes 1925. For 2040, subtract 12 from 20 to get 8:40 p.m.
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