Super Tens Addition: Leaping Over the Hundreds!

Hi Maths Masters! You’re doing great with adding tens. Now, let’s take it a step further! We’re going to mentally add multiples of 10 (like 20, 30, 40) to 3-digit numbers, but this time, our tens will be so powerful they’ll help us cross over into the next hundred! Imagine a sum like 385 plus 30. Let’s see how the hundreds change!

How to Add Tens Across the Hundreds (e.g., 385 + 30)

When the tens you’re adding are enough to make more than 10 tens in total, you create a new hundred!

Let’s break down 385 + 30:

Method 1: Bridging to the Next Hundred

• Our starting number is 385. We want to add 30 (which is 3 tens).
• Look at the tens in 385 – there are 8 tens. How many more tens do we need to add to 8 tens to make a new hundred (which is 10 tens)? We need 2 more tens (or 20).
• Let’s take those 2 tens (20) from the 30 we want to add.
  • So, 385 + 20 = 405. (The 8 tens plus 2 tens made 10 tens, which is a new hundred, changing 300 to 400. The 5 ones stay.)
• We wanted to add 30 in total, and we’ve already added 20. How much is left to add?
  • 30 − 20 = 10 (or 1 ten).
• Now, add that remaining 10 to our new number, 405.
  • 405 + 10 = 415.
• So, 385 + 30 = 415!

Method 2: Adding All the Tens Together

• In 385, we have 8 tens. We’re adding 30, which is 3 tens.
• Let’s add the tens digits: 8 tens + 3 tens = 11 tens.
• Now, 11 tens is the same as 1 hundred and 1 ten (because 10 tens = 1 hundred).
• So, this new “1 hundred” will add to the 3 hundreds already in 385, making it 3 + 1 = 4 hundreds.
• We have 1 ten left over from our “11 tens”.
• The 5 ones from 385 don’t change.
• So we have 4 hundreds, 1 ten, and 5 ones: 415.
• Therefore, 385 + 30 = 415!

Pick the method that feels like a maths superpower for you!

Your Brain Workout: 18 “Crossing the Hundreds with Tens” Sums!

Time to put those amazing brains to the test! Here are 18 questions where you’ll add multiples of 10 to a 3-digit number and cross into the next hundred. Think carefully about how those tens build up!

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

Why is This “Tens Crossing Hundreds” Skill So Powerful?

• Unlocks Bigger Calculations: This is a key step towards adding even larger numbers quickly.
• Improves Number Flexibility: You get really good at seeing how tens can become hundreds.
• Real-World Problem Solving: Helps when you’re adding amounts of money that go over £1, $1 etc., or measuring things in groups of 10.
• Makes You Feel Super Confident: Mastering this shows your amazing maths progress!

Guidance for Grown-Ups: Supporting This Skill

This activity helps children mentally add multiples of 10 to a 3-digit number where the sum of the tens results in regrouping into the hundreds place (e.g., 385 + 30 = 415; 170 + 50 = 220).

• Focus on “Making the Next Hundred”: The strategy of adding enough tens to reach the next hundred, then adding the remainder, is often very effective (Method 1).
• Place Value Understanding: Reinforce that 10 tens is equivalent to 1 hundred. Using base-ten blocks initially can help demonstrate this if children are unsure.
• Talk Through the Steps: Encourage children to explain how they arrived at their answer. This helps them consolidate their thinking.
• Relate to Simpler Facts: Connect 8 tens + 3 tens = 11 tens with 8 + 3 = 11.