Lesson 20 — Activity 1: Estimating and Measuring Time
Lesson 20 — Activity 1:
Estimating and Measuring Time
Lesson 20 — Activity 1:
Estimating and Measuring Time
If you have to be at school at 9 a.m., what time would you have
to leave in the morning if you are at your friend's house? Often we do
not have an exact answer, so we need to make an estimation, which is
essentially a guess of measurement.
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You may
remember that in previous math classes, you learned to add time. Adding
time is important, as it allows you to find out whether or not you can
finish all of your work in the time you have been given.
If you have to be at school at 9 a.m., what time would you have to leave in the morning if you are at your friend's house? Often we do not have an exact answer, so we need to make an estimation, which is essentially a guess of measurement.
For example, let's say you have two different tasks to do at your job. The first one takes 1 hour and 25 minutes to complete. The second one takes 4 hours and 10 minutes to complete. You have been given 6 hours at your job to complete both tasks. Will you have enough time?
To solve this question, you would do the following:
1. Add the minutes up first.
25 + 10 = 35 minutes
2. Add up the hours.
1 + 4 = 5 hours
3. Add the hours and minutes together.
5 hours + 35 minutes = 5 hours and 35 minutes
You have been given six hours to finish both tasks, so you have enough time!
Sometimes, it is quicker if you can estimate how much time something will take. We don't always need to know the exact number of hours and minutes something will take; we can sometimes give it our best estimate (educated guess)!
When we estimate time, we find an answer that is close to, but not exactly, the exact answer for a problem.
For example, say that you have been asked by your boss at work to cut 30 boards for a construction job. Your boss asks you if you will be able to have the job finished before the end of the day. It is currently 12:00 p.m. and you work until 5:00 p.m. Therefore, there are 5 hours left until the end of the day.
You have cut these types of boards before, and you know that it takes you about 8 minutes to cut each one. You can quickly do an estimate in your head so that you can give your boss an answer.
Remember, you don't have to be exact, and you know that it is easier to multiply by 10 than it is to multiply by 8.
So, you could quickly multiply:
10 (minutes per board) x 30 boards = 300 minutes.
You know that there are 60 minutes in an hour, so if you divide 300 minutes by 60 minutes, you get 5 hours.
It would take you about 5 hours to finish cutting all the boards, and that is how much time there is left until the end of the day. You can tell your boss that you have enough time to cut all 30 boards before the end of the day!
Let's try another example of where you might want to estimate numbers on the job.
You are working as a hairstylist at a local salon. One of your customers calls you to ask if you have time to fit her in for a quick cut at 3:00 p.m. It is now 12:17 p.m.
You are currently working with one of your customers doing a cut and colour. You have just started, and you know from experience that the cut and colour takes about 2 1/2 hours.
You could quickly do the estimate to see if you can fit her in as follows:
- It is currently 12:17 p.m., which is not an easy number to work with, so you could estimate the time to be 12:30 p.m., which will make it easier.
- If you add on the time that it will take you to finish your current appointment (which is 2 1/2 hours) to the current time of 12:30:
12:30 + 2 hours and 30 minutes = 3:00 p.m.
You will be finished your current appointment by 3:00 p.m., so you can fit in your next customer!
Another place where you might calculate time at your job is when you need to keep track of how many hours you worked on a time sheet. At the end of the week, you can total up all of your hours, and you will know about how much your cheque will be!
Look at the time sheet above. On Monday, February 8, Sally (the employee) started work at 5:00 p.m. and ended her shift at 9:25 p.m. In order to find out how many hours (and minutes) her shift was, she counted the minutes first, which was 25 minutes. Then she counted the hours from 5:00 to 9:00, which was 4 hours, and then she added these numbers together for a total of 4 hours and 25 minutes.
On the next day, Tuesday, February 9, Sally worked from 4:30 p.m to 9:10 p.m. To find out how many hours (and minutes) she worked, she first counted from 4:30 p.m. to 9:00 p.m., which is 4 hours and 30 minutes and then added on another 10 minutes because she worked until 10 minutes after nine, for a total of 4 hours and 40 minutes.
Now it's your turn! Go to the self-check activity below to practise counting the hours and minutes in the time sheet for the three missing days.
Self-check!
Try This!
Look at the time sheet above. Practise counting the hours and minutes that Sally worked for the following days on her time sheet:
Thursday, February 11
Saturday, February 13
Sunday, February 14
Try these on your own first, and then check your answers below.
Thursday, February 11 — 2:00 p.m. to 7:50 p.m.
If you count from 2:00 p.m. to 7:00 p.m., that gives you 5 hours of work, then you add on another 50 minutes for a total of 5 hours and 50 minutes.
Saturday, February 13 — 8:25 a.m. to 3:00 p.m.
If you count from 8:25 a.m. to 9:00 a.m., that gives you 35 minutes, then you count from 9:00 a.m. to 3:00 p.m., which gives you 6 hours, for a total of 6 hours and 35 minutes.
Sunday, February 14 — 10:00 a.m. to 2:40 p.m.
If you count from 10:00 a.m. to 2:00 p.m., that gives you 4 hours of work, then you add on another 40 minutes for a total of 4 hours and 40 minutes.