Elapsed Time Using Subtraction
Calculating the elapsed time means to find the difference between two times. To calculate the elapsed time, it is easiest to count up in hours. First find the number of minutes from the earliest time to the next hour by subtracting the number of minutes in the earliest time from 60.
Examples of Calculating Elapsed Time
Count up in hours until the hour before the final time. Then read the number of minutes from this hour until the final time.
Here, there are 40 minutes until 09:00, 1 hour until 10:00 and then 15 minutes from 10:00 until 10:15.
Adding the minutes, we have 1 hour 55 minutes.
The start and end times are labelled on the end of a time line.
Between 11:45 and 15:11 are the hours of 12:00, 13:00, 14:00 and 15:00, which are marked on the time line. We subtract the 45 minutes of 11:45 from 60 minutes to get 15 minutes.
Elapsed Time Word Problems
There are 15 minutes from 11:45 to 12:00. Between 12:00 and 15:00 there are 3 hours.
From 15:00 to 15:11 there are 11 minutes. We add the minutes together. 15 + 11 = 26 minutes in total. The elapsed time is 3 hours 26 minutes.
To calculate elapsed time:. Count the number of minutes from the first time to the hour that comes after it. Count on in hours until the hour immediately before the final time.
Count the number of minutes from this hour until the final time. Add the hours and minutes to find a total. For example, find the elapsed time between 11:45 and 15:11.
The first step is to count the number of minutes from the first time to the hour that comes after it.
The first time is 11:45 and the hour that comes after it is 12:00.
Each hour has 60 minutes and so, to work out the number of minutes between 11:45 and 12:00, subtract 45 from 60.
60 – 45 = 15 and so, there are 15 minutes between 11:45 and 12:00.
- The second step is to count on in hours until the hour immediately before the final time.
- From 12:00 until 15:00, there are 3 hours. The third step is to count the number of minutes from this hour until the final time.
From 15:00 until 15:11, there are 11 minutes. Simply read off the minutes from the final time. The final step is to add the hours and minutes to find a total.
There are 3 hours in total. Counting the minutes, 15 + 11 = 26.
The elapsed time is 3 hours and 26 minutes.
For example, calculate the elapsed time between 08:20 and 10:15.
First count 40 minutes from 08:20 until the next hour of 09:00.
Then count the 1 hour from 09:00 until 10:00.
Then count the 15 minutes from 10:00 to 10:15.
Adding the hours and minutes separately, the total elapsed time is 1 hour 15 minutes.
- Here is a set of examples of calculating the elapsed time between two given times.
- If the number of minutes in the final time is larger than the number of minutes in the start time, the elapsed time can be calculated by subtracting the start time from the final time.
- Subtract the hours and minutes separately.
How to Calculate the Elapsed Time
For example, between 10:22 and 23:57, we subtract the hours: 23 – 10 = 13. Then subtract the minutes: 57 – 22 = 35. The elapsed time is 13 hours and 35 minutes. The elapsed time can be calculated by direct subtraction only if the number of minutes in the final time is greater than the number of minutes in the start time.
- If this is not the case, negative numbers will arise if a larger number is subtracted from a smaller number.
- The formula for calculating elapsed time is elapsed time = end time – start time.
Subtract the minutes and hours separately. For example to calculate the elapsed time between 12:10 and 16:40, subtract 12:10 from 16:4.
Looking at the hours, 16 – 12 = 4 and looking at the minutes, 40 – 10 = 30. The elapsed time is 4 hours and 30 minutes.
To work out elapsed time on a number line, write the start time on the left of the line and the finish time on the right of the line.
The Formula for Calculating Elapsed Time
Write all of the hours in between these times on the number line.
Work out the minutes from the start time to the first hour and add this to the number of minutes from the last hour until the finish time.
Count the number of whole hours in between. For example, use a number line to find the elapsed time between 10:50 and 11:43.
First count on 10 minutes to get to 11:00 and then count on 43 minutes to get to 11:43.
Telling How Much Time Has Passed
In total, the elapsed time is 53 minutes. Here are some elapsed time worded problems. To solve word problems with elapsed time, identify the start and finish times.
Write these times at each end of a number line. Find the minutes from the start time to the next hour and from the final hour until the finish time.
Count the hours in between.
For example, “I start my homework at 18:30 and finish it at 19:13.
How long did it take to complete it?”. There are 30 minutes from the start time of 18:30 to the next hour and there are 13 minutes from 19:00 until 19:13.
The total minutes spent on the homework is 30 + 13, which equals 43 minutes. Here is another word problem involving calculating elapsed time.
“The bus leaves the station at 07:50 and arrives at its destination at 11:23. How long did the journey take?”. There are 10 minutes until the next hour of 08:00 and there are 23 minutes from 11:00 until 11:23.
Elapsed Time on a Number Line
In total, 10 + 23 = 33 minutes. There are also 3 hours between 08:00 and 11:00. The total elapsed time is 3 hours and 33 minutes. Now try our lesson on Negative Numbers on a Number Line where we learn about negative numbers.
Imagine running to the grocery store for some vegetables.
When you leave your house, the time is 2:05. When you come back, the time is 2:35.
Whenever you're figuring out how long something takes, you're finding the elapsedtime. Elapsedtime is the differencebetween two times.
An elapsed time is also called a timeinterval. Let's use our old friend the number line to help us find the time interval between 2:05 p.m.
Elapsed Time with Regrouping
You can show differences in time using numberlines! Numbers lines are pretty simple. They are a line with tickmarks. How much time should each tick mark represent? There are many good answers, but 5minutes seems convenient for our problem. Pick a starting time for the left most tick mark. If one tick mark is five minutes, then 3 tick marks represent 15 minutes. 👉 To find the interval between two times, plot them both on a number line:.
Then skipcount by 5 minutes for each tick mark. Tip: Instead of skip counting, you can also just count the number of tick marks between the two times, and multiply that by the value of each tick mark (5 min). There are 6 tick marks between the two times. The value of each tick mark is 5 minutes.
✅ So we figured out that the timeinterval between 2:05 and 2:35 is 30 minutes! Number lines are useful for finding elapsed time, or time intervals, but they're not very fast.
👉 Another way to find the elapsedtime is to subtract one time from the other. This is faster to do in your head.
Let's learn how to subtract two different times to find the time interval. Subtracting times is almost like subtracting numbers. Tip:When subtracting times, pick the later time as the minuend (or first number).
Just like with subtracting numbers, let's first subtract the smaller place values. 👉 Start by subtracting the minutes! Why not start with the hours? 🤔 There's no point subtracting the hours first, since you may need to borrowfrom the hours to solve the minutes. Remember: When you subtract, sometimes you have to regroup. So let's start with subtracting the minutes:.
Secret Trick: Find the Elapsed Time by Skip Counting
Yes, the time difference is 30 minutes! Now, we subtract the hours. So we see that your trip took 0 hours and 30 minutes! ✅ The elapsed time for your trip was 30 minutes! Now, let's say you saw a new superhero movie at the theater! The movie started at 7:20 and ended at 9:10.
How long was the movie? What should we do to find the elapsedtime? 👉 We can subtract the two times. Which time is our minuend? Yes, the bigger, later time! So let's think about the problem like this:.
Time Intervals and Number Lines
Do we start by subtracting the minutes, or the hours? We start with the minutes, because we may need to borrow from the hours.
It looks like we will need to borrow from the hours! SuperImportant: Every hour is 60 minutes, so when you borrow an hour, you add 60totheminutes!
Now we can solve the rest:. So, how long was your movie? ✅ Yes, it was 1 hour and 50 minutes long! Great job learning to find the elapsed time. Let's look at the last example again.
To figure this out quickly in your head, start by skipcounting the hours until you get close to the final time. After skip counting by 2 hours, we get pretty close to 9:10. So the elapsed time is pretty close to 2 hours.
Now, what do we have to do to turn 9:20 into the end time 9:10? Yes, we subtract 10 minutes! So we know our elapsed time is 2 hours minus 10 minutes. Let's solve this by regrouping one of the 2 hours into 60 minutes:. 2 hours - 10 minutes = ? We regroup 2 hours:. 1 hour + 60 minutes - 10 minutes = ?
Let's subtract the minutes:. ✅ Our elapsed time is 1 hour and 50 minutes!
We got the same answer by skip counting as we did by subtracting.
Now imagine your friend asks you:.
What time should you meet your friend at the playground? If you can subtract times, then you can also add them!
Let's add 1 hour and 30 minutes to 3:00 p.m.
Start by adding the minutes, because we may have to regroup them into hours. Now let's add the hour.
✅ So your friend wants to play at 4:30!
😺 You learned a lot about finding the elapsed time.
Now, complete the practice to help you remember for longer!
Elapsed time in simple terms is the amount of time that passes from the start of an event to its end.
In this lesson, you will learn how to solve for elapsed time and explore how it can be used in your everyday life. Say it is 3:15pm in the afternoon and you are to meet your friend at 6:25 pm.
Before you leave you should shower, get dressed, and have time to get to your friend's house. Now you must figure out in how much time you must finish your tasks and arrive at 6:25pm. Elapsed time is the amount of time that passes from the start of an event to its finish.
In simple terms, elapsed time is the time that goes by from one time (say 3:15pm) to another (6:25pm). The first thing you always do when solving for elapsed time is to find out your start time and end time.
Here, start time is 3:15 pm and end time is 6:25 pm. Looking at a clock, we know that the next hour to pass after start time 3:15 pm would be 4:00pm. So, counting from 3:15 to 4:00 there are 45 minutes between the two times. Similarly, counting from 6:00pm to 6:25pm, we see that there are 25 minutes between the two times. We have now to count the hours in the middle. We see that there are two hours between 4:00pm and 6:00pm.
The final step in finding out our elapsed time is to add together these durations. So, elapsed time. = 45 min + 2 hours + 25 min.
Key Facts and Summary
- = 70 min + 2 hours. = 1 hour + 2 hour + 10 min.
- = 3 hours 10 minutes.
- 1 minute = 60 seconds and 1 hour = 60 minutes
- A second is a very short period of time, say the time taken to blink your eye, to snap your fingers etc.
- A clock is an instrument to measure time which is shown in hours, minutes and seconds.
- Quarter of an hour = 60 ÷ 4 = 15 minutes
- Half of an hour = 60 ÷ 2 = 30 minutes.
- 12 :00 o’clock in the night is 12:00 midnight
- 12 :00 o’clock in the daytime is 12:00 noon
- We do not write a.m. or p.m. with 12:00 o’clock time.
- The numbers on the clock actually represent hours and the divisions between them represent the minutes.
- Second is the smallest unit and hour is the largest unit among the three units of time i.e. hour, minute and second. When the second hand moves once around the clock the minute hand moves through 1 minute
- The time between 12:00 midnight to 12:00 noon is written as a.m. Here a.m. means ante meridiem which means before midday.
- The time between 12:00 noon and 12:00 midnight is known as p.m. Here p.m. means post meridiem which means after midday.
- The hour hand of the clock goes round the clock in 12 hours.
- The minute hand completes one round in 1 hour.
- The second’s hand completes one round in 1 minute
- We can use the points on a number line as “ stepping stones ” and add on smaller “chunks of time” to find the total elapsed time.
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