Multiply by 1-Digit Numbers

Key Concepts

• Array multiplication
• Use place value for multiplication

Multiply by 1-digit numbers 

What are 1–digit numbers?  

The smallest one-digit number is 1 (one). 

The greatest one-digit number is 9.  

All the digits become numbers when used as a number. 

Example 1: 2 digits by 1–digit multiplication. 

Example 2: 2 digits by 1–digit multiplication. 

Multiply 8 × 26. 

Multiply the ones 8 × 6 = 48 

Multiply the tens 8 × 20 = 160 

Add the tens and ones. 

Array multiplication 

Example 1: 

A Ferris wheel completes a rotation for 38 seconds. How many seconds in all would it take to complete 4 rotations? 

Solution: 

One way to record multiplication.  

152 seconds will take to 4 rotations. 

Example 2: 

A polar bear climbs on a rock every morning to eat a breakfast of 29 fish. How many fish in one week will the polar bear eat?  

Solution: 

Multiply 29 × 7.  

Polar bear eats 203 fishes during the week. 

Use place value for multiplication 

At Kelvin’s birthday party, all his 4 friends get a surprise goodie bag. 38 candies are in each bag. How many candies do his friends get in all? 

Solution: 

Another way to record multiplication 

Step1: 

Multiply by the ones. 

Record the 2 ones. 

Record the 3 tens. 

Step 2: 

Multiply by the tens. 

His friends get 152 candies. 

Example 2: 

Charmin plays outside for 65 minutes in one day. How many minutes will she play in 8 days? 

Solution:  

She will get 520 minutes to play. 

Example 3: 

Tim bought 5 packs of balls. If each pack contains 134 balls, how many balls does Tim have in all?  

Solution: 

Multiply 134 × 5. 

Step 1: 

First multiply the ones. 

Step 2:  

Multiply the tens. 

Step 3:  

Multiply the hundreds 

So, 134×5 = 670. 

Tim has 670 balls. 

Exercise

• Find each product. Estimate to check if your answer is reasonable.  

  307

×   2

 553

×   3

• Find the product.

25

× 3

_________

_________

1172

×    4

• Use place value to explain each step to find 4 × 3, 678.

• Use the partial product model to find the product of 9 × 38

• Fill the missing numbers.

• Through the place value of multiplication, find the product.

• Ria ordered 9 boxes of fruits. There are 32 fruits in each box. How many fruits did ria order?
• A flashlight requires 2 batteries to function. How many batteries in all would 7 such
  flashlights require?
• Norah uses an ounce of butter to bake 9 cookies. How many cookies can she bake
  with 18 ounces of butter?
• A tour operator owns a small fleet of 8 cars of the same make. Each car is filled with
  2 liters of engine oil. How many liters in all have been filled in the cars?
• Vanessa sells 6 cakes every day. How many cakes will she sell in 20 days?

What have we learned

• Understand 1 digit numbers.
• Understand how to multiply by 1 digit through array model.
• Understand how to multiply by 1 digit through place value.
• Adding partial products.
• Identify the place value.

Concept Map