Addition and Subtraction of Whole Numbers Basic 6 Mathematics Lesson Note

a. Addition and Subtraction of Whole Numbers

Addition of Whole Numbers

Rules to Remember:

• Add from right to left (ones, tens, hundreds…)
• When sum is 10 or more, carry to the next column
• Write carried numbers small above the next column

Example: 345,678 + 156,789

  1 1 1    (carried numbers)

   345,678

 + 156,789

 ———

   502,467

Subtraction of Whole Numbers

Rules to Remember:

• Subtract from right to left
• When you can’t subtract, borrow from the next column
• Remember: borrowing makes the next digit smaller by 1

Example: 500,000 – 234,567

  4 9 9 9 9 10   (after borrowing)

   500,000

 – 234,567

 ———

   265,433

Exercise A – Whole Number Operations

Solve these problems:

1. 234,567 + 789,456 = __________
2. 1,234,567 + 876,543 = __________
3. 1,000,000 – 567,890 = __________
4. 5,678,901 – 2,345,678 = __________
5. 456,789 + 234,567 + 123,456 = __________

b. Addition and Subtraction of Decimal Fractions

Key Rule: Line up the decimal points!

Adding Decimals

Steps:

1. Write numbers with decimal points lined up
2. Add zeros if needed to make equal decimal places
3. Add normally from right to left
4. Bring down the decimal point

Example: 45.67 + 23.8 + 9.456

 45.670

  23.800

+  9.456

——–

  78.926

Subtracting Decimals

Steps:

1. Line up decimal points
2. Add zeros if needed
3. Subtract normally
4. Bring down decimal point

Example: 67.5 – 23.456

 67.500

– 23.456

——–

  44.044

Exercise B – Decimal Operations

Solve these problems:

1. 23.45 + 67.8 = __________
2. 156.789 + 23.45 + 8.9 = __________
3. 89.7 – 45.68 = __________
4. 200.0 – 156.789 = __________
5. 45.67 + 123.456 – 78.9 = __________

c. Real Problems on Addition and Subtraction

Money Problems

Example: Ade bought a shirt for ₦2,500.50, trousers for ₦4,200.75, and shoes for ₦6,800.00. How much did he spend altogether?

Solution: ₦2,500.50 + ₦4,200.75 + ₦6,800.00 = ₦13,501.25

Distance Problems

Example: Lagos to Ibadan is 128.5 km. Ibadan to Ilorin is 207.8 km. What is the total distance from Lagos to Ilorin via Ibadan?

Solution: 128.5 km + 207.8 km = 336.3 km

Exercise C – Money Word Problems

Solve these shopping problems:

1. Market Day: Mama Kemi bought rice for ₦5,600.00, beans for ₦2,300.50, and palm oil for ₦1,850.75. How much did she spend in total? Answer: ₦__________
2. Pocket Money: Tunde has ₦8,450.25 in his savings box. His father gives him ₦2,500.00 more. If he spends ₦4,750.50 on books, how much is left? Answer: ₦__________
3. Business Profit: A trader sold goods worth ₦45,600.75 on Monday and ₦38,250.50 on Tuesday. If her expenses were ₦15,890.25, what was her profit? Answer: ₦__________

Exercise D – Distance and Measurement

Solve these problems:

1. School Journey: Kemi walks 1.5 km from home to the bus stop, travels 12.8 km by bus to school. What is her total journey to school? Answer: __________ km
2. Farming: A farmer’s land is 456.75 meters long. He extends it by 123.5 meters. What is the new length? Answer: __________ meters
3. Construction: A building is 45.8 meters tall. A 12.75-meter antenna is added on top. What is the total height? Answer: __________ meters

Exercise E – Population and Large Numbers

Solve these problems:

1. City Population: Kano has 4,103,000 people and Lagos has 15,388,000 people. What is their combined population? Answer: __________
2. School Statistics: Government College has 2,567 students. 234 new students join while 156 graduate. What is the new total? Answer: __________

d. Quantitative Reasoning

Mental Math Tricks

Adding 9s: Add 10, then subtract 1

• 67 + 9 = 67 + 10 – 1 = 77 – 1 = 76

Subtracting 9s: Subtract 10, then add 1

• 85 – 9 = 85 – 10 + 1 = 75 + 1 = 76

Adding near hundreds: Round up, then adjust

• 456 + 99 = 456 + 100 – 1 = 556 – 1 = 555

Number Patterns

Example: 5, 12, 19, 26, ___ Pattern: Add 7 each time Next number: 26 + 7 = 33

Exercise F – Mental Mathematics

Solve using mental math tricks:

1. 78 + 19 = ______ (Add 20, subtract 1)
2. 145 – 29 = ______ (Subtract 30, add 1)
3. 67 + 98 = ______ (Add 100, subtract 2)
4. 234 – 99 = ______ (Subtract 100, add 1)

Exercise G – Number Patterns

Find the pattern and complete:

1. 15, 23, 31, 39, ______, ______ Pattern: ______
2. 2.5, 5.0, 7.5, 10.0, ______, ______ Pattern: ______
3. 100, 93, 86, 79, ______, ______ Pattern: ______
4. 1.2, 2.4, 3.6, 4.8, ______, ______ Pattern: ______

Exercise H – Estimation

Round to nearest 100 and estimate, then calculate exactly:

1. Problem: 567 + 234 Estimate: ______ + ______ = ______ Exact: ______
2. Problem: 789 – 345 Estimate: ______ – ______ = ______ Exact: ______
3. Problem: 23.7 + 45.9 Estimate: ______ + ______ = ______ Exact: ______

Exercise I – Logic Problems

Use reasoning to solve:

1. Missing Number: A + 567 = 1,234. What is A? Answer: A = ______
2. Balance Problem: Three boxes weigh 12.5 kg, 18.7 kg, and 23.8 kg. What is their total weight? Answer: ______ kg
3. Money Problem: I had some money. I spent ₦2,450 and have ₦3,670 left. How much did I start with? Answer: ₦______

Exercise J – Real-World Reasoning

Apply mathematical thinking:

1. Time Problem: A movie is 2 hours 45 minutes long. If it starts at 3:30 PM, what time will it end? Answer: ______
2. Shopping List: Items cost ₦1,250, ₦980, ₦2,340, and ₦567. You have ₦6,000. Do you have enough money? How much change will you get? Answer: ______
3. Sports Score: Team A scored 2, 4, 1, and 3 goals in four matches. Team B scored 1, 3, 4, and 2 goals. Which team scored more goals and by how much? Answer: ______

Exercise K – Problem Solving

Think and solve:

1. Puzzle: The sum of two numbers is 789. If one number is 345, what is the other number? Answer: ______
2. Planning: A school needs 1,250 chairs. They already have 567 chairs. How many more chairs do they need to buy? Answer: ______
3. Savings Goal: Bola wants to save ₦50,000. She has saved ₦23,750 so far. How much more does she need to save? Answer: ₦______

Answer Key

Exercise A:

1. 1,024,023
2. 2,111,110
3. 432,110
4. 3,333,223
5. 814,812

Exercise B:

1. 91.25
2. 189.139
3. 44.02
4. 43.211
5. 90.226

Exercise C:

1. ₦9,751.25
2. ₦6,199.75
3. ₦67,961.00

Exercise D:

1. 14.3 km
2. 580.25 meters
3. 58.55 meters

Exercise E:

1. 19,491,000
2. 2,645 students

Exercise F:

1. 97
2. 116
3. 165
4. 135

Exercise G:

1. 47, 55 (add 8)
2. 12.5, 15.0 (add 2.5)
3. 72, 65 (subtract 7)
4. 6.0, 7.2 (add 1.2)

Exercise I:

1. A = 667
2. 55.0 kg
3. ₦6,120