Lesson 11: Money - 1

For Grade 5 Students (Ages 10-11) - Let's learn about money and its value!

What we will learn today:

In this lesson, you will learn to:

  • Identify Sri Lankan currency (rupees and cents).
  • Convert between rupees and cents.
  • Add and subtract amounts of money.
  • Solve simple word problems involving money.

Introduction to Money

Hello, young mathematicians! Money is something we use every day to buy things we need and want, like food, clothes, and toys. It comes in different forms, like coins and banknotes.

In Sri Lanka, our currency is the **Rupee (Rs.)** and **Cents (cts.)**. Just like how we have meters and centimeters for length, we have Rupees and Cents for money!

Let's learn about our money and how to use it for calculations.

Sri Lankan Currency: Rupees and Cents

Sri Lankan money consists of:

  • **Coins:** $1, 2, 5, 10$ rupees, and $25, 50$ cents (though cents are less commonly used now).
  • **Banknotes (Paper Money):** $20, 50, 100, 500, 1000, 2000, 5000$ rupees.

Key Conversion:

  • $1$ Rupee (Rs.) = $100$ Cents (cts.)

Converting Rupees and Cents

We can convert between rupees and cents just like we converted between meters and centimeters.

Example 1: Convert Rs. $5$ to cents.

Since Rs. $1$ = $100$ cts., then Rs. $5$ = $5 \times 100 = 500$ cts.

Example 2: Convert $750$ cents to rupees and cents.

Since $100$ cts. = Rs. $1$, then $750$ cts. = $700$ cts. + $50$ cts. = Rs. $7$ and $50$ cts.

Exercise 1: Convert the following amounts.

Rs. $8$ = $\underline{\hspace{2cm}}$ cts.

$400$ cts. = $\underline{\hspace{2cm}}$ Rs.

Rs. $12$ and $25$ cts. = $\underline{\hspace{2cm}}$ cts.

$1575$ cts. = $\underline{\hspace{1cm}}$ Rs. $\underline{\hspace{1cm}}$ cts.

Adding and Subtracting Money

When adding or subtracting money, always align the rupees and cents columns. Remember to regroup (carry over or borrow) $100$ cents as $1$ rupee, or $1$ rupee as $100$ cents.

Example 3: Add Rs. $25.50$ and Rs. $10.25$.

    Rs. 25.50
+   Rs. 10.25
-----------
    Rs. 35.75

Add cents: $50 + 25 = 75$ cts.
Add rupees: $25 + 10 = 35$ Rs.
Total: Rs. $35.75$

Example 4: Subtract Rs. $12.75$ from Rs. $30.50$.

    Rs. 30.50  -> Rs. 29.150 (borrow 1 Rupee = 100 cents)
-   Rs. 12.75
-----------
    Rs. 17.75

We cannot subtract $75$ cts. from $50$ cts. So, we borrow Rs. $1$ from $30$ Rs. (making it $29$ Rs.) and add $100$ cts. to $50$ cts., making it $150$ cts.
Now, $150 - 75 = 75$ cts.
And $29 - 12 = 17$ Rs.
Total: Rs. $17.75$

Exercise 2: Add or subtract the following amounts.

Rs. $45.20$ + Rs. $15.30$ = $\underline{\hspace{1cm}}$ Rs. $\underline{\hspace{1cm}}$ cts.

Rs. $7.80$ + Rs. $3.50$ = $\underline{\hspace{1cm}}$ Rs. $\underline{\hspace{1cm}}$ cts.

Rs. $60.75$ - Rs. $20.25$ = $\underline{\hspace{1cm}}$ Rs. $\underline{\hspace{1cm}}$ cts.

Rs. $50.00$ - Rs. $18.50$ = $\underline{\hspace{1cm}}$ Rs. $\underline{\hspace{1cm}}$ cts.

Problem Solving with Money

Let's solve some real-life problems involving money.

Exercise 3: Solve the following word problems.

  1. You have Rs. $150.00$. You buy a book for Rs. $75.50$. How much money do you have left?

  2. Amal earns Rs. $250.00$ and his sister Nimali earns Rs. $175.50$. How much money do they earn together?

  3. A toy car costs Rs. $350.00$. If you pay with a Rs. $500.00$ note, how much change will you get?

Answers to Practice Time

Let's check your answers!

  1. Exercise 1: Converting Amounts

    • Rs. $8$ = $800$ cts.
    • $400$ cts. = Rs. $4$
    • Rs. $12$ and $25$ cts. = $1225$ cts.
    • $1575$ cts. = Rs. $15$ $75$ cts.

  2. Exercise 2: Adding and Subtracting Amounts

    • Rs. $45.20$ + Rs. $15.30$ = Rs. $60.50$
    • Rs. $7.80$ + Rs. $3.50$ = Rs. $11.30$ (since $80+50=130$ cts. = Rs. $1.30$)
    • Rs. $60.75$ - Rs. $20.25$ = Rs. $40.50$
    • Rs. $50.00$ - Rs. $18.50$ = Rs. $31.50$

  3. Exercise 3: Problem Solving with Money

    • Rs. $150.00 - 75.50 = 74.50$. You have Rs. $74.50$ left.
    • Rs. $250.00 + 175.50 = 425.50$. They earn Rs. $425.50$ together.
    • Rs. $500.00 - 350.00 = 150.00$. You will get Rs. $150.00$ change.

You've completed Lesson 11!

Fantastic work, Math Lanka students! You've learned all about money, from identifying currency to performing calculations and solving real-world problems. Keep practicing to become smart with money!

Next Lesson
Previous Lesson Next Lesson