What is Adding and Subtracting Time in Hours?

S1-SA4-0363

Grade Level:

Class 2

All STEM domains, Finance, Economics, Data Science, AI, Physics, Chemistry

Definition

What is it?

Adding and subtracting time in hours means combining different time durations or finding the difference between them. We treat hours like regular numbers for addition and subtraction, but remember that there are 60 minutes in an hour.

Simple Example

Quick Example

Imagine you are watching a cricket match that starts at 2 PM and lasts for 3 hours. To find out when the match will finish, you would add 3 hours to 2 PM. So, 2 PM + 3 hours = 5 PM.

Worked Example

Step-by-Step

Question: Your school bus journey takes 1 hour. If you leave home at 7 AM, what time will you reach school?

Step 1: Identify the starting time and the duration to add. Starting time = 7 AM. Duration = 1 hour.
---Step 2: Add the hours directly to the starting time. 7 + 1 = 8.
---Step 3: Keep the AM/PM part the same unless you cross noon or midnight. Since 7 AM + 1 hour is still morning, it remains AM.
---Answer: You will reach school at 8 AM.

Why It Matters

Understanding how to add and subtract time is crucial for planning schedules, managing projects, and even in fields like data science for analyzing time-series data. Pilots use it for flight plans, and event managers use it to organize events smoothly.

Common Mistakes

MISTAKE: Treating hours and minutes as one big number (e.g., 1 hour 30 minutes + 30 minutes = 1 hour 60 minutes, then saying it's 1 hour 60 minutes). | CORRECTION: Remember that 60 minutes make 1 hour. So, 1 hour 60 minutes should be converted to 2 hours.

MISTAKE: Forgetting to adjust AM/PM when crossing noon (12 PM) or midnight (12 AM). | CORRECTION: When you add hours and cross 12, the AM/PM changes (e.g., 10 AM + 3 hours = 1 PM, not 13 AM).

MISTAKE: Directly subtracting larger hours from smaller hours without borrowing or adjusting. | CORRECTION: If you need to subtract 3 hours from 2 PM, you can think of it as 14:00 (24-hour format) minus 3 hours = 11:00, which is 11 AM.

Practice Questions

Try It Yourself

QUESTION: Your favourite TV show starts at 6 PM and lasts for 1 hour. What time will it finish? | ANSWER: 7 PM

QUESTION: A train journey is 4 hours long. If the train departs at 9 AM, what time will it reach its destination? | ANSWER: 1 PM

QUESTION: You started studying for your exams at 3 PM. You took a break after 2 hours. After your break, you studied for another 1 hour. What time did you finish studying in total? | ANSWER: 6 PM

MCQ

Quick Quiz

Your family plans to go to the market. They leave home at 10 AM and spend 2 hours there. What time will they finish shopping?

1899-12-30T11:00:00.000Z

1899-12-30T12:00:00.000Z

1899-12-30T13:00:00.000Z

1899-12-30T14:00:00.000Z

The Correct Answer Is:

If they leave at 10 AM and spend 2 hours, you add 2 hours to 10 AM, which gives you 12 PM. Options A, C, and D are incorrect calculations.

Real World Connection

In the Real World

From planning your daily schedule for school and homework to booking a flight or train ticket, adding and subtracting time is used everywhere. Even delivery apps like Zepto or Swiggy use this to estimate how long your order will take to reach you, helping their delivery partners manage their routes efficiently.

Key Vocabulary

Key Terms

ADDITION: Combining quantities together | SUBTRACTION: Finding the difference between quantities | DURATION: The length of time that something continues | AM: Ante Meridiem, refers to the time from midnight to noon | PM: Post Meridiem, refers to the time from noon to midnight

What's Next

What to Learn Next

Great job with adding and subtracting time in hours! Next, you can learn about adding and subtracting time in hours AND minutes. This will help you manage even more precise schedules, like planning your study breaks or cooking times.