Lesson 7: Multiplication - 1

For Grade 5 Students (Ages 10-11) - Let's learn to multiply numbers!

What we will learn today:

In this lesson, you will learn to:

  • Understand multiplication as repeated addition.
  • Multiply numbers by a single-digit number.
  • Multiply numbers by $10, 100,$ and $1000$.
  • Solve simple word problems involving multiplication.

Introduction to Multiplication

Welcome, young mathematicians! After learning about addition, subtraction, and number patterns, it's time to explore another important operation: multiplication.

Multiplication is a quick way of doing repeated addition. For example, if you have 3 groups of 4 apples, you can add $4+4+4$ or simply multiply $3 \times 4$. Both give you the same answer!

Let's learn how to multiply numbers efficiently.

Multiplication by Single-Digit Numbers

To multiply a number by a single-digit number, we multiply each digit of the larger number by the single-digit number, starting from the Ones place and moving left. We carry over if needed, just like in addition.

Example 1: Multiply $123$ by $3$.

    123
  x   3
  -----
    369

Here:
$3 \times 3 = 9$ (Ones)
$3 \times 2 = 6$ (Tens)
$3 \times 1 = 3$ (Hundreds)
So, $123 \times 3 = 369$.

Example 2: Multiply $245$ by $4$.

    245
  x   4
  -----
    980

Here:
$4 \times 5 = 20$ (Write $0$, carry over $2$ to Tens)
$4 \times 4 = 16$. Add carried $2$: $16 + 2 = 18$ (Write $8$, carry over $1$ to Hundreds)
$4 \times 2 = 8$. Add carried $1$: $8 + 1 = 9$ (Write $9$)
So, $245 \times 4 = 980$.

Exercise 1: Multiply the following numbers.

$34 \times 2 = \underline{\hspace{2cm}}$

$156 \times 3 = \underline{\hspace{2cm}}$

$728 \times 5 = \underline{\hspace{2cm}}$

$1045 \times 6 = \underline{\hspace{2cm}}$

Multiplication by $10, 100,$ and $1000$

Multiplying by $10, 100,$ or $1000$ is very easy! You just need to add zeros to the end of the number.

Rule:

  • To multiply by $10$, add one zero ($0$) to the end of the number.
  • To multiply by $100$, add two zeros ($00$) to the end of the number.
  • To multiply by $1000$, add three zeros ($000$) to the end of the number.

Examples:

  • $25 \times 10 = 250$
  • $7 \times 100 = 700$
  • $12 \times 1000 = 12000$

Exercise 2: Multiply the following numbers.

$58 \times 10 = \underline{\hspace{2cm}}$

$9 \times 100 = \underline{\hspace{2cm}}$

$34 \times 1000 = \underline{\hspace{2cm}}$

$120 \times 100 = \underline{\hspace{2cm}}$

Problem Solving with Multiplication

Multiplication is very useful for solving real-life problems.

Exercise 3: Solve the following word problems.

  1. A box contains $12$ pencils. If you buy $5$ such boxes, how many pencils do you have in total?

  2. A bus can carry $45$ passengers. If $8$ buses are full, how many passengers are there in total?

  3. A factory produces $250$ toys per hour. How many toys will it produce in $10$ hours?

Answers to Practice Time

Let's check your answers!

  1. Exercise 1: Multiplication by Single-Digit Numbers

    • $34 \times 2 = 68$
    • $156 \times 3 = 468$
    • $728 \times 5 = 3640$
    • $1045 \times 6 = 6270$

  2. Exercise 2: Multiplication by $10, 100,$ and $1000$

    • $58 \times 10 = 580$
    • $9 \times 100 = 900$
    • $34 \times 1000 = 34000$
    • $120 \times 100 = 12000$

  3. Exercise 3: Problem Solving with Multiplication

    • $12 \times 5 = 60$ pencils in total.
    • $45 \times 8 = 360$ passengers in total.
    • $250 \times 10 = 2500$ toys will be produced.

You've completed Lesson 7!

Excellent work, Math Lanka students! You've successfully learned the basics of multiplication. Keep practicing your multiplication facts, and you'll be a math whiz in no time!

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