Adding and Subtracting Big Numbers

Happy Tuesday, Grade 5s!

Today in class, we talked about strategies for doing "mental math" with big numbers. We spent most of our time talking about rounding numbers to the nearest hundred, and then adding or subtracting them.

For example:
If I needed to subtract 5793 from 8452 (8452-5793), I could round both numbers to the nearest hundred.
Let's start with 8452. To round to the nearest hundred, I'm going to look at the digit in the TENS column. If that digit is 5 or greater, I will round UP. If the digit in the tens column is less than 5, I will round DOWN.
The digit is 5, so we will round up to 8500.

Now let's look at 5793. I need to look at the number in the tens column, which is a 9. I know I need to round UP to 5800.

Now I can subtract: 8500-5800=2700.

Super Challenge:
Try this to challenge yourself:

75426341+42568772

The first person to post the answer on the blog wins a prize tomorrow in class!

Good luck!

Remember, if you have any questions about tonight's homework, or today's lesson, post them here and I'll write you back.

See you tomorrow!

-Ms. Lewis.