## Key Concepts

- Use partial products
- Use the standard algorithm

## What are the 3-digit numbers?

100 to 999 are the 3-digit numbers.

100 is the smallest 3-digit number.

999 is the largest 3-digit number.

### How to multiply a 3-digit number with a 2-digit number?

- Multiply by the number in the ones place.

- Put a zero below in the ones place.

- Multiply by the number in the tens place.

- Add them up.

For example, 324 × 46

## Use partial products

**Example 1:**

In an auditorium, there are 493 rows with 14 seats in each row. How many seats are available?

**Solution: **

Multiply 493 × 14

**6, 902 seats are available. **

**Example 2:**

Lenin bought a school bag. A bag cost is $ 236. Find the cost of 47 such bags?

**Solution:**

Multiply 236 × 47

**47 bags cost $11,092. **

### Use the standard algorithm

**Example 1:**

Charmin took her 735 students to the cricket stadium. Admission for each student was $24. What was the total amount of money needed?

**Solution:**

**Step 1:** To use the standard algorithm, first multiply by the ones, regroup as needed.

4 × 5 ones= 20 ones or 2 tens

4 × 3 tens = 12 tens

12 tens + 2 tens = 14 tens.

14 tens = 1 hundred 4 tens.

4 × 7 hundred = 28 hundreds.

28 hundred + 1 hundred = 29 hundred.

**Step 2:** Multiply by the tens regroup as needed.

20 × 5 ones =100 ones

20 × 3 tens = 60 tens or 6 hundred.

20 × 7 hundreds = 140 hundreds or 14 thousand.

**Step 3**: Add to get the final product

**$17, 640 amount was needed. **

**Example 2:**

Robert ordered 134 boxes of magnetics. There were 35 magnetic balls in each box. How many magnetic balls did he order?

**Solution:**

**Step 1:** To use the standard algorithm, first multiply by the ones, regroup as needed.

5 × 4 ones= 20 ones or 2 tens

5 × 3 tens = 15 tens

15 tens + 2 tens = 17 tens.

17 tens = 1 hundred 7 tens.

5 × 1 hundred = 5 hundreds.

5 hundred + 1 hundred = 6 hundred.

**Step 2:** Multiply by the tens regroup as needed.

30 × 4 ones =120 ones

30 × 3 tens = 90 tens or 9 hundred.

30 × 1 hundreds = 30 hundreds or 3 thousand.

3 thousand +1 thousand = 4 thousands.

**Step 3**: Add to get the final product.

**Step 3**: Add to get the final product.

**He ordered 4,690 magnetic balls.**

## Exercise

- Find each product. Estimate to check your answer is reasonable.

a. 3 1 5 b. 4 9 6

× 7 7 × 1 6

_________ _________

_________ _________

- Use partial products to find the product.

a. 8 6 7 b. 5 4 8

× 6 3 × 8 6

_________ _________

_________ _________

- Use standard algorithm model to find the product.

a. 9 9 1 b. 5 4 0

× 4 4 × 5 1

_________ _________

_________ _________

- Determine the missing digit in the following multiplication.

a. 3 8 2

× __ 4

_________

16,808

_________

- Determine the missing digit in the following multiplication.

- Find the product. Estimate to check for reasonableness.

a. 3 7 2

× 4 3

_________

_________

- Last month bakery sold 345 boxes of cupcakes. Each box has 15 cupcakes. How many cakes did the store sell in the last month? Find 15 x 345.
- Sally shoots an arrow 130 yards. Flame shoots her arrow 12 times as far. How far did Flame’s arrow go
- Mother bought 35 large packets of spearmint bubble gum. If each packet contains pieces, how many pieces are there altogether?
- Laura sells home-made pizza sauce. If she uses 19 tomatoes to make one jar of sauce, how many tomatoes do she need to make 115 jars?

### What have we learned

- Understand 3 digit numbers.
- Understand partial products.
- Multiplying 3-digit number by 2 digit numbers through partial product model.
- Identify the partial products.
- Multiplying 3-digit number by 2 digit numbers through standard algorithm model.

### Concept Map