Hundreds High-Five! Adding Big Groups of 100!

Hello Mighty Mathematicians! Get ready to work with some really big numbers today! We’re going to learn how to mentally add multiples of 100 (like 200, 300, or 400) to 3-digit numbers. This is a super cool skill because it shows you how powerful the hundreds place is! Let’s try a sum like 245 plus 300.

How to Add Multiples of 100 (e.g., 245 + 300)

When we add a multiple of 100 (like 100, 200, 300, etc.), the magic happens mostly in the hundreds place of our 3-digit number. The tens and ones digits usually just stay put!

Let’s look at 245 + 300:

• Our starting number is 245. This has 2 hundreds, 4 tens, and 5 ones.
• We want to add 300. That’s the same as 3 hundreds.
• So, we just need to add the hundreds together: 2 hundreds + 3 hundreds = 5 hundreds.
• What about the tens and ones? In 245, we have 4 tens and 5 ones. When we add 300, we’re not adding any extra tens or ones.
• So, the 4 tens stay as 4 tens.
• And the 5 ones stay as 5 ones.
• Putting it all together: 5 hundreds, 4 tens, and 5 ones makes 545.
• That means 245 + 300 = 545. See? Only the hundreds digit changed!

This makes adding hundreds mentally quite straightforward once you focus on that hundreds place!

Your Turn: 18 “Add the Hundreds” Challenges!

Ready to give it a go? Here are 18 mental maths questions. In each one, you’ll add a multiple of 100 to a 3-digit number. Remember to keep an eye on that hundreds digit!

(Your web app with the 18 questions will go here.)

Why is Adding Multiples of 100 an Awesome Skill?

• Boosts Place Value Power: You become a real expert at understanding hundreds, tens, and ones.
• Foundation for Bigger Maths: This helps you get ready to add and subtract even larger numbers.
• Makes Estimating Easier: You can quickly get a good idea of answers to bigger sums.
• Everyday Connections: Useful when thinking about distances, weights, or larger amounts of money.

Pointers for Parents & Teachers

This activity is designed to help children confidently add multiples of 100 to a 3-digit number mentally, focusing on how only the hundreds place value is affected (e.g., 245 + 300 = 545; 618 + 200 = 818).

• Isolate the Hundreds Digit: Encourage children to identify the hundreds digit in both numbers and add them first.
• Keep Tens and Ones Constant: Explicitly point out that the tens and ones digits from the original 3-digit number remain unchanged in these types of problems.
• Use Base-Ten Blocks (If Needed): Physically adding bundles of 100 (flats) to a representation of the 3-digit number can make the concept very clear for visual and kinaesthetic learners.
• Connect to Simpler Facts: Remind them that 2 hundreds + 3 hundreds is just like 2 + 3, but they are groups of a hundred.