# 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

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