This video tutorial teaches how to subtract numbers within 100 using an open number line. It begins with an introduction to friendly numbers and their role in simplifying subtraction. The lesson reviews number building and skip counting by tens. It then introduces open number lines as a tool for subtraction, providing examples and practice problems to illustrate the concept. The tutorial emphasizes the non-commutative nature of subtraction and demonstrates how to decompose numbers to make subtraction easier.

What is a friendly number and why is it useful in subtraction?

• A number that is always odd

• A number that is a multiple of 10, making subtraction easier

• A number that is easy to add

• A number that is always even

Which of the following is true about subtraction?

• Subtraction is not commutative

• Subtraction is commutative like addition

• Subtraction always results in a larger number

• Subtraction can be done in any order

How can an open number line help in subtraction?

• By adding numbers together

• By making numbers larger

• By helping you visualize the subtraction process

• By allowing you to count forwards

When subtracting 9 from 57 using an open number line, what is the first step?

• Subtract 9 directly

• Subtract 7 to reach a friendly number

• Add 9 to 57

• Subtract 5 to reach a friendly number

In the example of subtracting 8 from 72, how is the number 8 decomposed?

• Into 7 and 1

• Into 5 and 3

• Into 4 and 4

• Into 2 and 6