Numeracy

Calculating with Time




1. Basic Units of Time

  • Second (s): SI unit of time.
  • Minute: 60 seconds. Occasionally 61 seconds (leap seconds).
  • Hour: 60 minutes.
  • Day: 24 hours.
  • Week: 7 days (work week = 5 days).
  • Month: 28, 29, 30, or 31 days (varies).
  • Year: 12 months (365 days or 366 in a leap year).
  • Larger units: Decade (10 years), Century (100 years), Millennium (1,000 years).

Tip: Months to weeks: divide by 12, multiply by 52.
Weeks to months: divide by 52, multiply by 12.

2. Writing Time

  • 24-hour clock: 00:00 (midnight) to 23:59. Common in military and seafaring contexts.
  • 12-hour clock: Divided into am (before noon) and pm (after noon).

Examples:
- 16:10 (24-hour) = 4:10 pm (12-hour).
- Times like "ten past twelve" or "quarter to three" are common in spoken English.

3. Calculating Time Passed

Steps:
1. Convert times into 24-hour format for consistency.
2. Subtract using hours, minutes, and seconds separately.
3. Break calculations into manageable parts:
- Minutes to the next hour.
- Whole hours between times.
- Remaining minutes to the target time.
4. Add these parts together.

Example:
- Start: 11:44 Next train: 13:17.
- Minutes from 11:44 to 12:00 = 16.
- Hours from 12:00 to 13:00 = 1.
- Minutes from 13:00 to 13:17 = 17.
- Total wait = 1 hour 33 minutes.

4. Adding Time Across Sessions

To calculate total time:
1. Add all minutes together.
2. Convert extra minutes (>60) into hours.
3. Add whole hours.

Example: Gardening job over 3 days:
- Day 1: 3h 25m, Day 2: 2h 50m, Day 3: 1h 15m.
- Total minutes: 25 + 50 + 15 = 90 (convert to 1h 30m).
- Total hours: 3 + 2 + 1 = 6.
- Total time: 7h 30m (7.5 hours).

Earnings at $10/hour: 7.5 × 10 = $75.

5. Tools for Accuracy

  • Use scientific calculators with degree/minute/second (DMS) functions.
  • Always verify if the answer seems reasonable based on the context.

Key Tip: When calculating, double-check alignment with expected outcomes to catch errors!

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