# ADDITION AND SUBTRACT UNITS OF TIME

LESSON PLANNING OF ADDITION AND SUBTRACT UNITS OF TIME WITH CARRYING/BORROWING

Subject Mathematics

Students` Learning Out coming

• Add and subtract units of time with carrying/borrowing.

Information for Teachers

• The same units are added i.e.
• o   Hours can be added  to hours; 3:hours + 9 hours

o   Minutes can be added to minutes; e.g.: 25 minutes +m 32 minutes.

o   Second can be added to seconds; : 33 seconds + 21 seconds +

• If two different units of time are given then one will be converted into the other before adding, For example;

o   6 hours + 72 minutes

o   6 x 60 = 360 minutes

o   360 minutes + 72 minutes = 432 minutes

o   Again convert it in hours and minutes by divide with 60 x 432 ÷ 60 = hours 20 minutes.

• For Subtraction of time:

• The same traditional method of carrying will be used, but carrying will be done from hours or minutes as 60.
• For example; (30 + 60 = 90) carry 1 hour i.e. 60 minutes

4 hours 30 minutes

-3 hour 45 minutes

Ans: 45 minutes

• We will use some units, like : 36 seconds + 12 seconds
• If we get different units like 4 minutes + 2 seconds then convert minutes in seconds then add them.
• For subtraction if the top number is less than bottom number then we borrow,1 from previous number like 1 hours 20 minutes -30 minutes =?
• During this lesson, for all steps, the teacher should refer thee book according to the requirements.

Material / Resources

Writing board, chalk / marker, duster, textbook

Introduction

• Ask: “is this addition or subtraction?” [How much left, means subtraction]

Let them try and find answer

Write their answer on the board

Development

Activity 1

Teacher`s input:

• Times aren`t in base 10, so you have to think carefully about what borrowing means; Times are in base 60(which is what the ancient Babylonians used for all their math)
• Write on the board 1: 30 minus 0:7 minutes.
• If one hour is equal to 60 minutes then one and a half hour = 60 +30 = 90 minutes. So we can subtract 90 – 75 = 5 = 15 minutes.

Group Work:

• Working in groups, ask them to create two time subtraction questions and write on the sheets.
• Don`t forget to write the names of the peers on the sheets back of the sheet.
• Allocate time.
• Announce students’ names and attempt the question on the board.

It`s my turn (Pair work)

• Working in the pairs asks them to do few time subtraction sums.
•  Allocate reasonable time
• Allocate questions from the textbooks
• Share some questions with the whole class for reinforcement.

Teacher`s input:

• 10 minutes plus 5 minutes is what? [Students will say 15 minutes]
• OK, 20 minutes plus 20 minutes? [40 minutes]
• 30 minutes plus 30 minutes is what? [60 minutes]
• Say: “one hour instead of 60 minutes” [because 1 hour = minutes, so we present in bigger unit]
• Ask: “how do we change that, 45 minutes + 45 minutes =? [ some would say 90 minutes]
• Write on the board 45 minutes + 45 minutes = 90 minutes.., since it`s greater than 60, so w subtract 60 from the answer and carry 60 minutes as 1 hour to the hour`s side, hence the answer will be? [1 hour and 30 minutes]
• Conclude: the way to do it is similar to the way that you add and subtract regular numbers; the difference is that with “borrow” or “carrying” numbers between the hours and seconds.

Subtraction of time:

Teacher`s input:

• Teacher will explain that:
• o   You first subtract the minutes.
• o   If the top minute number is less than the bottom number, you first borrow an hour from top hour number, reducing that number by 1.
• Once you have borrowed 1, you then add 60 to the top minute number, and then do the subtraction. Then, you go over to the hour`s part and subtract those numbers.

Pair Work:

• What time will be after 45 minutes? [Give them time to solve this table]
• Once the time is up, invite pairs to come and explain on the board.
• Share with the whole class and announce “pair of the day” having correct answer.
• May repeat one more time that when the sum is more than 60 minutes? We add one hour in the hours and exclude 60 minutes.

Activity 3

• What time would it be before 45 minutes?
• Change the pairs, if before they were working with the peer sitting next to them, now ask to turn around and work with the peer sitting at the back. If now it is 45 minutes before it was 12:30 pm.

• Once the time is up, invite pairs to come and explain on the board.
• Share with whole class and announce the title “pair of the day for subtraction” for the pairs with all correct answers.
• Repeat one more time that when the lower number is greater than the above we borrow one hour and add 60 minutes to the upper values.

Sum up / Conclusion

• Tell: One good thing about addition and subtraction is that it can give you a better understanding of carrying and borrowing.
• Borrowing and carrying in a regular arithmetic practice, i.e. exchanging 10 units for a ten [ or tens for a hundred, etc.]
• Borrowing and carrying in time mean exchanging 60 minutes for an hour.
• Ask: “who will tell us what we have done up-till now?”
• Student: “we have done addition and subtraction of time. In the begging we did some mental math questions regarding time.”

Assessment

• After extensive revision on board and as pair work, now it is the time for individual assignment.
• Announce that this individual work will be marked later for assessment, as well.
• Give questions from the textbook for both addition and subtraction.
• Announce time.
• Collect notebooks to be checked later.

• Teacher must also involve the students in solving the exercise questions give at the end of the lesson of the textbook.