What is Adding and Subtracting Durations?

S1-SA4-0414

Grade Level:

Class 3

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

Definition

What is it?

Adding and subtracting durations means combining or finding the difference between lengths of time. We use this to figure out how long an activity lasts or when something will start/end.

Simple Example

Quick Example

Imagine you watch a cricket match that starts at 10:00 AM and lasts for 3 hours. To find out when it ends, you add the duration (3 hours) to the start time (10:00 AM). The match ends at 1:00 PM.

Worked Example

Step-by-Step

PROBLEM: Your school bus journey takes 45 minutes in the morning and 30 minutes in the afternoon. How much total time do you spend on the bus each day?

STEP 1: Identify the durations to be added: 45 minutes and 30 minutes.

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STEP 2: Add the minutes together: 45 + 30 = 75 minutes.

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STEP 3: Convert the total minutes into hours and minutes, if needed. Since 60 minutes make 1 hour, 75 minutes is 1 hour and 15 minutes (75 - 60 = 15).

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ANSWER: You spend 1 hour and 15 minutes on the bus each day.

Why It Matters

Understanding durations is crucial in planning your day, from school timetables to travel schedules. It's used by pilots to calculate flight times, by event managers to plan festivals, and even by scientists to track experiments.

Common Mistakes

MISTAKE: Treating minutes like regular base-10 numbers (e.g., 30 minutes + 40 minutes = 70 minutes, then writing it as 1 hour 10 minutes, but doing 30 + 40 = 70 and then 70-60 = 10, so 1 hour 10 minutes). | CORRECTION: Remember there are 60 minutes in an hour, not 100. When minutes add up to 60 or more, convert the 'extra' 60 minutes into 1 hour and carry it over.

MISTAKE: Forgetting to convert units when necessary (e.g., adding hours to minutes directly without converting). | CORRECTION: Always make sure all time units are the same (all minutes, or all hours, or convert to hours and minutes) before adding or subtracting.

MISTAKE: Subtracting smaller minutes from larger minutes without borrowing correctly from hours. | CORRECTION: If you need to subtract, say, 40 minutes from 10 minutes, borrow 1 hour (60 minutes) from the 'hours' column, making it 70 minutes, then subtract.

Practice Questions

Try It Yourself

QUESTION: A train journey from Delhi to Jaipur takes 4 hours and 30 minutes. If the train departs at 7:00 AM, when will it reach Jaipur? | ANSWER: 11:30 AM

QUESTION: Your favourite TV show starts at 8:00 PM and ends at 8:45 PM. How long is the show? | ANSWER: 45 minutes

QUESTION: Riya studied for 1 hour and 20 minutes in the morning and then for 55 minutes in the evening. How much total time did she study? | ANSWER: 2 hours and 15 minutes

MCQ

Quick Quiz

A movie started at 6:15 PM and had a duration of 2 hours and 30 minutes. When did the movie end?

1899-12-30T20:30:00.000Z

1899-12-30T20:45:00.000Z

1899-12-30T21:00:00.000Z

1899-12-30T21:15:00.000Z

The Correct Answer Is:

Adding 2 hours to 6:15 PM gives 8:15 PM. Then, adding 30 minutes to 8:15 PM gives 8:45 PM. So, the movie ended at 8:45 PM.

Real World Connection

In the Real World

Delivery apps like Zomato or Swiggy use duration calculations to tell you 'estimated delivery time'. They add the time taken to prepare food and the travel time to give you an accurate estimate, helping you plan your meal.

Key Vocabulary

Key Terms

DURATION: The length of time that something lasts | ELAPSED TIME: The amount of time that has passed between two points in time | CARRY OVER: Moving an amount from one column to the next when adding | BORROW: Taking an amount from the next higher place value when subtracting

What's Next

What to Learn Next

Now that you understand adding and subtracting durations, you can explore 'Time Zones' to learn how different parts of the world experience different times. This builds on your understanding of time calculations on a global scale.