In this activity, we will **add **or **subtract 100, 10 or 1** to or from a number.

When we add or subtract **100**, it is the **hundreds **digit that we change.

When we add or subtract **10**, it is the **tens **digit that we change.

When we add or subtract **1**, it is the **ones **digit that we change.

Remember that *other *digits may have to change too.

**Example 1**

What number is **100** **less **than **750**?

**Answer**

**Reduce 7 hundred** by 1 hundred to get **6 hundred**...

750 becomes **650**

**Example 2**

What number is **10 more** than **539**?

**Answer**

**Increase** **3 tens** by 1 ten to get **4 tens**...

539 becomes** 549**

**Example 3**

What number is **1 less** than **539**?

**Answer**

**Reduce** **9 ones** by 1 one to get** 8 ones**...

539 becomes** 538**

**Example 4**

What number is **10 less** than **405**?

__Answer__

Here we have to be careful, because we can't reduce the tens digit by 1.

So include the hundreds digit.

Think of it as **reducing ****40 tens** by 1 ten to get** 39 tens**.

405 becomes **395**

That was a hard one to finish with, so make sure you've understood it before attempting the questions.

You can look back at this introduction at any point by clicking on the red help button on the screen.