Hundreds Countdown! Subtracting Big Groups of 100!

Hi Maths Adventurers! Ready to tackle some big number subtractions? Today, we’re learning how to mentally subtract multiples of 100 (like 200, 300, or 400) from 3-digit numbers. Just like when we added hundreds, this skill is all about focusing on the hundreds place, making it simpler than you might think! Let’s try a sum like 765 take away 400.

How to Subtract Multiples of 100 (e.g., 765 − 400)

When we subtract a multiple of 100 (like 100, 200, 300, etc.) from a 3-digit number, the main change happens in the hundreds place. The tens and ones digits often just stay exactly where they are!

Let’s look at 765 − 400:

• Our starting number is 765. This has 7 hundreds, 6 tens, and 5 ones.
• We want to subtract 400. That’s the same as 4 hundreds.
• So, we just need to subtract the hundreds: 7 hundreds − 4 hundreds = 3 hundreds.
• What about the tens and ones? In 765, we have 6 tens and 5 ones. When we subtract 400, we’re not taking away any extra tens or ones.
• So, the 6 tens stay as 6 tens.
• And the 5 ones stay as 5 ones.
• Putting it all back together: 3 hundreds, 6 tens, and 5 ones makes 365.
• That means 765 − 400 = 365. See? Only the hundreds digit changed!

As long as the hundreds digit in your starting number is big enough, this is a straightforward mental calculation!

Your Turn: 18 “Subtract the Hundreds” Challenges!

Ready to practise this cool skill? Here are 18 mental maths questions. In each one, you’ll subtract a multiple of 100 from a 3-digit number. Keep your eye on that hundreds digit and watch it change!

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

Why is Subtracting Multiples of 100 a Super Skill?

• Strengthens Place Value Understanding: You become an expert at seeing how hundreds, tens, and ones work.
• Key for Bigger Subtraction: This helps you get ready to subtract even larger numbers with confidence.
• Improves Estimation: You can quickly guess the rough answer to more complex subtraction problems.
• Real-World Maths: Useful when figuring out differences in prices, distances, or when a large amount is taken away from a total.

Helpful Hints for Parents & Teachers

This activity helps children develop confidence in mentally subtracting multiples of 100 from a 3-digit number, by focusing on the change in the hundreds place value while the tens and ones remain constant (e.g., 765 − 400 = 365; 582 − 200 = 382).

• Focus on the Hundreds Digit: Encourage children to first identify the hundreds digit in both numbers and perform the subtraction there.
• Tens and Ones Stay Put: Clearly point out that in these types of problems, the tens and ones digits of the original 3-digit number do not change.
• Use Visuals if Necessary: Base-ten blocks (physically removing bundles of 100) or a number line (making large jumps of 100 backwards) can support understanding for some learners.
• Link to Basic Facts: Remind children that 7 hundreds − 4 hundreds is just like 7 − 4, but applied to groups of one hundred.