Addition and Subtraction of Money for Primary 4

Money (1)

Performance Objectives

By the end of the lesson, students should be able to:

1. solve problems in addition of money;
2. solve problems on subtraction of money;
3. solve quantitative aptitude problems involving addition and subtraction of money.

Understanding Money

Money is a medium of exchange used to buy goods and services. In Nigeria, the currency is the Naira (₦) and Kobo (k). One Naira is equal to one hundred Kobo (₦1 = 100k).

Money comes in different forms, such as banknotes (paper money) and coins. It is important to know how to count, add, and subtract money correctly to manage personal finances and make purchases.

Addition of Money

Adding money means combining two or more amounts of money to find a total. When adding money, it is important to align the Naira and Kobo parts correctly. The Naira amounts are added together, and the Kobo amounts are added together.

If the sum of the Kobo is 100 or more, 100 Kobo is converted to ₦1 and carried over to the Naira column. The remaining Kobo is written in the Kobo column.

Steps for Adding Money

1. Write the amounts of money in columns, ensuring that the Naira (₦) values are under Naira and the Kobo (k) values are under Kobo. A decimal point can be used to separate Naira and Kobo, like ₦150.50.
2. Add the Kobo amounts first.
3. If the sum of the Kobo is 100 or more, divide it by 100. Write the remainder in the Kobo column and carry over the quotient (the whole number part) to the Naira column.
4. Add the Naira amounts, including any amount carried over from the Kobo column.

Worked Examples of Addition of Money

Example 1: Add ₦250.75 and ₦130.20.

Solution:

$$
\begin{array}{r}
₦250.75 \\
+₦130.20 \\
\hline
₦380.95
\end{array}
$$

First, add the Kobo: $75k + 20k = 95k$. Write 95 in the Kobo column.

Next, add the Naira: $₦250 + ₦130 = ₦380$. Write 380 in the Naira column.

The total is ₦380.95.

Example 2: Add ₦475.60 and ₦325.80.

Solution:

$$
\begin{array}{r}
₦475.60 \\
+₦325.80 \\
\hline
₦801.40
\end{array}
$$

First, add the Kobo: $60k + 80k = 140k$.

Since $140k = ₦1$ and $40k$, write 40 in the Kobo column and carry over ₦1 to the Naira column.

Next, add the Naira: $₦475 + ₦325 + ₦1$ (carried over) $= ₦801$. Write 801 in the Naira column.

The total is ₦801.40.

Example 3: A mother bought rice for ₦1,500.50 and beans for ₦850.75. How much did she spend in total?

Solution:

Cost of rice = ₦1,500.50

Cost of beans = ₦850.75

Total cost = Cost of rice + Cost of beans

$$
\begin{array}{r}
₦1500.50 \\
+₦850.75 \\
\hline
₦2351.25
\end{array}
$$

First, add the Kobo: $50k + 75k = 125k$.

Since $125k = ₦1$ and $25k$, write 25 in the Kobo column and carry over ₦1 to the Naira column.

Next, add the Naira: $₦1500 + ₦850 + ₦1$ (carried over) $= ₦2351$. Write 2351 in the Naira column.

The mother spent ₦2,351.25 in total.

Subtraction of Money

Subtracting money means finding the difference between two amounts of money. When subtracting money, it is important to align the Naira and Kobo parts correctly. The Kobo amounts are subtracted from Kobo, and Naira amounts are subtracted from Naira.

If the Kobo amount to be subtracted is larger than the Kobo amount it is being subtracted from, ₦1 (which is 100 Kobo) is borrowed from the Naira column and added to the Kobo column before subtracting.

Steps for Subtracting Money

1. Write the amounts of money in columns, ensuring that the Naira (₦) values are under Naira and the Kobo (k) values are under Kobo.
2. Subtract the Kobo amounts first.
3. If the Kobo amount in the top number is smaller than the Kobo amount in the bottom number, borrow ₦1 (which is 100 Kobo) from the Naira column. Add 100 Kobo to the top Kobo amount, then subtract.
4. Subtract the Naira amounts, remembering to reduce the top Naira amount by ₦1 if you borrowed from it.

Worked Examples of Subtraction of Money

Example 1: Subtract ₦120.30 from ₦350.75.

Solution:

$$
\begin{array}{r}
₦350.75 \\
-₦120.30 \\
\hline
₦230.45
\end{array}
$$

First, subtract the Kobo: $75k – 30k = 45k$. Write 45 in the Kobo column.

Next, subtract the Naira: $₦350 – ₦120 = ₦230$. Write 230 in the Naira column.

The difference is ₦230.45.

Example 2: Subtract ₦280.90 from ₦500.50.

Solution:

$$
\begin{array}{r}
₦500.50 \\
-₦280.90 \\
\hline
₦219.60
\end{array}
$$

First, subtract the Kobo: We cannot subtract $90k$ from $50k$.

Borrow ₦1 from the Naira column (₦500 becomes ₦499). Add 100 Kobo to the 50 Kobo, making it $150k$.

Now, $150k – 90k = 60k$. Write 60 in the Kobo column.

Next, subtract the Naira: $₦499 – ₦280 = ₦219$. Write 219 in the Naira column.

The difference is ₦219.60.

Example 3: John had ₦7,500.00. He spent ₦3,250.80 on a new school bag. How much money does he have left?

Solution:

Money John had = ₦7,500.00

Money spent = ₦3,250.80

Money left = Money John had – Money spent

$$
\begin{array}{r}
₦7500.00 \\
-₦3250.80 \\
\hline
₦4249.20
\end{array}
$$

First, subtract the Kobo: We cannot subtract $80k$ from $00k$.

Borrow ₦1 from the Naira column (₦7500 becomes ₦7499). Add 100 Kobo to the 00 Kobo, making it $100k$.

Now, $100k – 80k = 20k$. Write 20 in the Kobo column.

Next, subtract the Naira: $₦7499 – ₦3250 = ₦4249$. Write 4249 in the Naira column.

John has ₦4,249.20 left.

Quantitative Aptitude Problems Involving Addition and Subtraction of Money

Quantitative aptitude problems are word problems that require using both addition and subtraction of money to find a solution. These problems often involve multiple steps and require careful reading to understand what is being asked.

Worked Examples of Quantitative Aptitude Problems

Example 1: A trader bought oranges for ₦1,200.50 and sold them for ₦1,850.00. How much profit did the trader make?

Solution:

Cost of oranges = ₦1,200.50

Selling price of oranges = ₦1,850.00

Profit = Selling price – Cost price

$$
\begin{array}{r}
₦1850.00 \\
-₦1200.50 \\
\hline
₦649.50
\end{array}
$$

First, subtract the Kobo: We cannot subtract $50k$ from $00k$.

Borrow ₦1 from the Naira column (₦1850 becomes ₦1849). Add 100 Kobo to the 00 Kobo, making it $100k$.

Now, $100k – 50k = 50k$. Write 50 in the Kobo column.

Next, subtract the Naira: $₦1849 – ₦1200 = ₦649$. Write 649 in the Naira column.

The trader made a profit of ₦649.50.

Example 2: Mary had ₦5,000.00. She bought a storybook for ₦750.25 and a pencil case for ₦300.50. How much money does she have left?

Solution:

Step 1: Find the total amount Mary spent.

Cost of storybook = ₦750.25

Cost of pencil case = ₦300.50

Total spent = Cost of storybook + Cost of pencil case

$$
\begin{array}{r}
₦750.25 \\
+₦300.50 \\
\hline
₦1050.75
\end{array}
$$

Mary spent ₦1,050.75 in total.

Step 2: Subtract the total amount spent from the money Mary had.

Money Mary had = ₦5,000.00

Money left = Money Mary had – Total spent

$$
\begin{array}{r}
₦5000.00 \\
-₦1050.75 \\
\hline
₦3949.25
\end{array}
$$

First, subtract the Kobo: We cannot subtract $75k$ from $00k$.

Borrow ₦1 from the Naira column (₦5000 becomes ₦4999). Add 100 Kobo to the 00 Kobo, making it $100k$.

Now, $100k – 75k = 25k$. Write 25 in the Kobo column.

Next, subtract the Naira: $₦4999 – ₦1050 = ₦3949$. Write 3949 in the Naira column.

Mary has ₦3,949.25 left.

Wise Spending of Money

Spending money wisely means making good choices about how to use money. It involves planning, prioritising needs over wants, and saving for important things. Wise spending helps people manage their money effectively and avoid running out of it too quickly.

Ways to Spend Money Wisely

To spend money wisely, consider the following:

1. Make a list: Before going to the market or shop, make a list of things that are truly needed. This helps to avoid buying unnecessary items.
2. Prioritise needs: Needs are things essential for living, such as food, water, shelter, and school supplies. Wants are things that are nice to have but not essential, like toys or extra snacks. Always buy needs first.
3. Compare prices: Look at different shops or stalls to find the best prices for items. This helps to save money.
4. Save some money: It is wise to save a portion of any money received. This saved money can be used for future needs or emergencies.
5. Avoid impulse buying: Do not buy things just because they look attractive at the moment. Think carefully if the item is truly needed.
6. Budgeting: Plan how much money to spend on different items. For example, decide how much to spend on food, how much on transport, and how much to save.

By following these steps, people can make smart choices with their money and ensure it is used for important things.