Sophia wants to add and subtract 1 and 10 from the numbers she sees. Can you help her find the sums and differences?

We will use a hundred chart to help us add and subtract 1 and 10 from each number. A hundred chart shows the numbers from 1 to 100. It is very helpful when we want to find and use number patterns!

When we want to add or subtract 1 or 10, there are number patterns we will follow to find the sums and differences.

To add 1, move to the right one box on the chart. This is like adding a penny or a unit block.

To subtract, move to the left one box on the chart. This is like taking away a penny or a unit block.

To add 10 to a number, move down one box on the chart.

This is just like adding a dime or a rod.

To subtract 10, move up one box on the chart. This is like taking away a dime or a rod.

Are you ready to help Sophia add and subtract 1 and 10?

Sophia wants to start with the number 15. Let’s add 1 to and subtract 1 from 15. First, we need to find 15 on the hundred chart. Where is 15 on the hundred chart?

Here! Now we can use the patterns we know to add and subtract 1. Which direction do we need to move on the chart to add 1?

To the right! When we move one box to the right, we land on the box with 16 in it. 15 plus 1 equals 16!

Which direction do we need to move to subtract 1?

To the left! When we move one box to the left, we land on the box with 14 in it. 15 minus 1 equals 14!

Sophia wants to add 10 to and subtract 10 from the number 27. Where is 27 on the hundred chart?

Yes! Now we can use the patterns we know to add and subtract 10. Which direction do we need to move on the chart to add 10?

Down! When we move down one box, we land on the box with 37 in it. 27 plus 10 equals 37!

Which direction do we need to move to subtract 10?

Up! When we move up one box, we land on the box with 17 in it. 27 minus 10 equals 17!

Now let’s add 1 to and subtract 1 from the number 49. Where is 49 on the hundred chart?

Yes! Let’s add 1 first. Which box do we need to move to?

The box with 50 in it! 50 is one box to the right of 49. 49 plus 1 equals 50!

Now we can subtract 1. What box do we need to move to?

The box with 48 in it! 48 is one box to the left of 49. 49 minus 1 equals 48!

Let’s add 1 to and subtract 1 from 70. Here is 70 on the chart. Let’s add 1 first. Which box do we need to move to?

Wait, there isn’t a box to the right of 70! What do we do? Move down a row and start with the first box. Which number is in the first box of the next row?

71! 70 plus 1 equals 71!

Now we can subtract 1. Which box do we need to move to?

The box with 69 in it! 69 is one box to the left of 70. 70 minus 1 equals 69!

Thank you for your help adding and subtracting using the hundred chart! Sophia is excited that she can add and subtract 1 and 10 from any number she sees!