Adding two and three digit numbers

Adding two and three digit numbers

using an open number line

lets review place value first

...

568

Let's look at the ones, tens and hundreds place.

What number is represented in the model?

which digit is in the ones, tens and hundreds place?

Now that we have review place value let's use place value to add large numbers!

535 + 240 =

When solving addition equations with an open number line, we start by putting the larger addend on the left end of the number line. The larger addend in the addition equation 535 + 240 = ___ is 535. Write that number to the far left on the number line. Now, we can add.

535 + 240 =

We can break apart the smaller addend, 240, into its expanded form. It will help us add on the number line. We can break the number 240 into 2 hundreds, 4 tens, and 0 ones. This makes the number 200 + 40. 

535 + 240 =

We need to add 200, which is 2 hops of 100. Remember that when we add 100 to a number, we only add 1 to the hundreds place. We take one hop of 100 to 635 and another hop of 100 to 735.  Now, we need to add 40 from the tens place.

535 + 240 =

We need to add 4 tens on our number line. When we add tens, we are increasing the number in the tens place by 1 each time we hop. Start at 735 and hop 4 tens. 745, 755, 765, 775. After adding our 200 and 40, we land on 775. This means that we have solved the addition equation. So, 535 + 240 = 775.