Time | Fourth Grade
Complete Notes & Formulas
1. Convert Time Units
Definition: Converting time units means changing between seconds, minutes, hours, days, weeks, and years using conversion factors.
⏰ Time Conversion Chart:
| Time Unit | Conversion |
|---|---|
| 1 minute | = 60 seconds |
| 1 hour | = 60 minutes = 3,600 seconds |
| 1 day | = 24 hours |
| 1 week | = 7 days |
| 1 year | = 365 days (366 in leap year) = 52 weeks = 12 months |
📝 Conversion Rules:
- Larger to Smaller: Multiply (hours→minutes: ×60)
- Smaller to Larger: Divide (minutes→hours: ÷60)
✏️ Examples:
Convert 3 hours to minutes:
3 hours = 3 × 60 = 180 minutes
Convert 240 seconds to minutes:
240 seconds = 240 ÷ 60 = 4 minutes
2. Add and Subtract Mixed Time Units
Definition: Mixed time units combine hours and minutes (like 2 hours 30 minutes). Adding and subtracting requires converting when needed.
➕ Adding Mixed Time Units:
- Step 1: Add minutes to minutes
- Step 2: If minutes ≥ 60, convert to hours (60 min = 1 hour)
- Step 3: Add hours including any converted hours
✏️ Addition Example:
Problem: 2 hours 45 minutes + 1 hour 30 minutes
Solution:
Hours: 2 + 1 = 3 hours
Minutes: 45 + 30 = 75 minutes
Convert: 75 min = 1 hour 15 minutes
Total: 3 hours + 1 hour 15 minutes
Answer: 4 hours 15 minutes
➖ Subtracting Mixed Time Units:
- Subtract minutes from minutes
- If top minutes < bottom minutes, borrow 1 hour (60 min)
- Subtract hours
3. A.M. or P.M.
Definition: A.M. (ante meridiem) means "before noon" and P.M. (post meridiem) means "after noon". They help us distinguish between morning and evening times.
🌅 Understanding A.M. and P.M.:
A.M. (Ante Meridiem) - Before Noon
• Midnight to just before noon
• 12:00 A.M. (midnight) to 11:59 A.M.
• Morning activities: breakfast, school starts
P.M. (Post Meridiem) - After Noon
• Noon to just before midnight
• 12:00 P.M. (noon) to 11:59 P.M.
• Afternoon/evening activities: lunch, dinner, bedtime
📝 Key Points:
- 12:00 A.M. = Midnight (start of day)
- 12:00 P.M. = Noon (middle of day)
- One complete day = 12 hours A.M. + 12 hours P.M. = 24 hours
4. Elapsed Time
Definition: Elapsed time is the amount of time that has passed between a start time and an end time.
🔑 Key Formulas:
Elapsed Time = End Time - Start Time
End Time = Start Time + Elapsed Time
Start Time = End Time - Elapsed Time
📝 Methods to Calculate Elapsed Time:
Method 1: Number Line (Timeline)
Draw a line, mark start time, count forward to end time
Method 2: Subtraction
Subtract start time from end time (borrow 60 min if needed)
✏️ Example:
Problem: Movie starts at 3:30 PM and ends at 5:45 PM. How long is the movie?
Solution (Number Line):
3:30 PM → 4:00 PM = 30 minutes
4:00 PM → 5:00 PM = 1 hour
5:00 PM → 5:45 PM = 45 minutes
Total: 30 min + 1 hour + 45 min = 1 hour 75 min = 2 hours 15 minutes
Answer: 2 hours 15 minutes
5. Find Start and End Times: Multi-Step Word Problems
Definition: Multi-step time problems involve finding unknown start times or end times using given information about duration and other times.
📝 Problem-Solving Steps:
- Step 1: Identify what you know (start, end, or elapsed time)
- Step 2: Identify what you need to find
- Step 3: Choose the correct formula
- Step 4: Solve step by step
- Step 5: Check if answer makes sense
✏️ Examples:
Example 1: Find End Time
Problem: Class starts at 9:15 AM and lasts 1 hour 30 minutes. What time does it end?
Solution:
9:15 AM + 1 hour = 10:15 AM
10:15 AM + 30 minutes = 10:45 AM
Answer: 10:45 AM
Example 2: Find Start Time
Problem: A concert ended at 8:30 PM. It lasted 2 hours 45 minutes. What time did it start?
Solution:
Work backward: 8:30 PM - 2 hours = 6:30 PM
6:30 PM - 45 minutes = 5:45 PM
Answer: 5:45 PM
6. Convert Between 12-Hour and 24-Hour Time
Definition: 12-hour clock uses A.M. and P.M. (1-12). 24-hour clock (military time) goes from 00:00 to 23:59 without A.M./P.M.
🕐 12-Hour to 24-Hour Conversion:
A.M. Times (12:01 AM - 11:59 AM):
• 12:01 AM - 12:59 AM → 00:01 - 00:59 (replace 12 with 00)
• 1:00 AM - 11:59 AM → 01:00 - 11:59 (keep same, add 0 if single digit)
P.M. Times (12:00 PM - 11:59 PM):
• 12:00 PM - 12:59 PM → 12:00 - 12:59 (keep same)
• 1:00 PM - 11:59 PM → Add 12 to the hour (1+12=13, 2+12=14, etc.)
📝 Conversion Table:
| 12-Hour | 24-Hour | 12-Hour | 24-Hour |
|---|---|---|---|
| 12:00 AM | 00:00 | 12:00 PM | 12:00 |
| 3:00 AM | 03:00 | 3:00 PM | 15:00 |
| 8:30 AM | 08:30 | 8:30 PM | 20:30 |
✏️ Examples:
• 7:45 AM → 07:45 (24-hour)
• 4:30 PM → 4+12 = 16:30 (24-hour)
• 19:00 → 19-12 = 7:00 PM (12-hour)
7-8. Transportation Schedules (12-Hour & 24-Hour Time)
Definition: Transportation schedules show arrival and departure times of buses, trains, or flights. They can be in 12-hour or 24-hour format.
🚌 Sample Bus Schedule (12-Hour Format):
| Stop | Bus A | Bus B | Bus C |
|---|---|---|---|
| City Center | 8:00 AM | 10:30 AM | 2:15 PM |
| Main Street | 8:25 AM | 10:55 AM | 2:40 PM |
| Station | 8:45 AM | 11:15 AM | 3:00 PM |
📝 How to Read Schedules:
- Find the departure location (row)
- Find the bus/train number (column)
- Look where row and column meet for time
- Calculate travel time by subtracting departure from arrival
✏️ Example Problem:
Question: Using Bus A, how long does it take from City Center to Station?
Solution:
Departure: 8:00 AM
Arrival: 8:45 AM
Travel Time: 8:45 - 8:00 = 45 minutes
Answer: 45 minutes
9. Time Patterns
Definition: Time patterns involve sequences of times that follow a rule, like adding the same amount of time repeatedly.
📝 Types of Time Patterns:
Pattern Type 1: Adding Same Duration
Example: 2:00, 2:30, 3:00, 3:30, __
Rule: Add 30 minutes each time
Next: 4:00
Pattern Type 2: Subtracting Same Duration
Example: 5:00 PM, 4:30 PM, 4:00 PM, __
Rule: Subtract 30 minutes each time
Next: 3:30 PM
Pattern Type 3: Regular Intervals
Example: Events every 45 minutes starting at 9:00 AM
Times: 9:00, 9:45, 10:30, 11:15, 12:00
📝 Steps to Solve Time Patterns:
- Look at the first few times in the sequence
- Find the difference between consecutive times
- Check if the difference is the same (rule)
- Apply the rule to find next times
✏️ Practice Example:
Pattern: 7:15 AM, 8:00 AM, 8:45 AM, __, __
Solution:
Find difference: 8:00 - 7:15 = 45 minutes
Check: 8:45 - 8:00 = 45 minutes ✓
Rule: Add 45 minutes each time
Next: 8:45 + 45 min = 9:30 AM
Then: 9:30 + 45 min = 10:15 AM
Answer: 9:30 AM, 10:15 AM
Time Quick Reference Chart
| Concept | Key Formula/Rule |
|---|---|
| Time Conversion | 1 hour = 60 min, 1 day = 24 hours |
| Elapsed Time | End Time - Start Time |
| End Time | Start Time + Elapsed Time |
| Start Time | End Time - Elapsed Time |
| A.M. | Midnight to noon (12:00 AM - 11:59 AM) |
| P.M. | Noon to midnight (12:00 PM - 11:59 PM) |
| 12 to 24 Hour (PM) | Add 12 to hour (3 PM = 15:00) |
| 24 to 12 Hour | If >12, subtract 12 and add PM |
⏰ Essential Time Conversions:
1 minute = 60 seconds
1 hour = 60 minutes
1 day = 24 hours
1 week = 7 days
1 year = 365 days
1 year = 52 weeks
📚 Fourth Grade Time - Complete Study Guide
Master these time concepts for everyday math excellence! ✨