Subtracting

Subtracting using the counting back strategy on an open number line

...

Place Value

We're going to review place value before we use an open number line to subtract large numbers. Let's get started!

Multiple Choice

How many hundreds, tens and ones are in the number 743?

• 7 hundreds 4 tens 3 ones

• 3 hundreds 4 tens 7 ones

Multiple Select

Which place value is the digit 4 in the number 485 in?

• hundreds

• tens

• ones

Multiple Choice

If I subtracted 550 - 10 which place value would change?

• hundreds

• tens

• ones

Multiple Select

If I added 873 + 100

Which place value would change?

• hundreds

• tens

• ones

800 - 300 =

When we are finding the difference between two numbers we can use the count back strategy on an open number line. when we make an open number line, we starting by drawing a straight line with arrows on each end. When we subtract, we place the larger number at the far right of the line with a tick, and green dot to show where we are starting. In our equation, 800 is the larger number.

800 - 300 =

We want to subtract 300, which is 3 hundreds. This is 3 hops of 100, counting back from 800. We know that when we subtract by hundreds, only the number in the hundreds place changes, and it decreases. We hop back 3 and count. We say 700, 600, 500. We land on 500, and that is where we stop. We mark our landing place with a red dot.We solved the equation by using an open number line, and we found that 800 – 300 = 500.

Multiple Choice

900 - 300 =

Use your counting back strategy on an open number line.

• 1,200

• 600

900 - 300 = 600

When using the counting back strategy where should you start on the number line, with 900 or 600?

How many jumps did you take to get from 900 to 600?

860 - 210 =

Let's start by putting the larger number, 860, on the far right of the number line. We will use a green dot to show where we are starting. 

860 - 210 =

We are subtracting 210 from 860, so we can break apart 210 into 200 and 10, which is 2 hundreds and 1 ten. 

860 - 210 =

On our open number line, we will count back 2 hops of 100, or 200. We count back and say 760, 660. So, 860 – 200 = 660.

Now, we need to count back 1 ten. Count and hop back to 650. We landed on 650, so we draw a red dot to show where we landed. We have solved to find that 860 – 210 = 650.

Multiple Choice

530 - 220 = ?

Use your counting back strategy on an open number line.

• 750

• 310

530 - 220 = 310

When you break apart 220 into hundreds, tens and ones, how many of each group will you end up with?

How many jumps did you take to get from 530 to 220?