Adding Multiples of 10 Mentally

Year 3 Mathematics Building Number Sense Mental Maths Strategies

Learning Objectives

Add multiples of 10 to any 3-digit number mentally Understand what happens when we cross into the next hundred Use number bonds to 100 to help with calculations Recognise patterns in place value when adding multiples of 10

Quick Fire Starter

Count in 10s from different starting numbers 42, 52, 62, 72... What comes next? Try starting from 156, 267, 389

What Do We Already Know?

We can count in 10s: 10, 20, 30, 40... 10 is made of 1 ten and 0 ones 100 is made of 10 tens We know our number bonds to 10 and 20

Place Value: The Key to Mental Addition

Adding 10 to 2-Digit Numbers

Start with what we know: 23 + 10 = 33 Only the tens digit changes The ones digit stays the same Try: 45 + 10, 67 + 10, 89 + 10

What Happens Here?

What is 97 + 10? Think about crossing into the next hundred Which digits will change? Can you explain your thinking to a partner?

Crossing the Hundred Boundary

When we add 10 to 97, we get 107 We need to regroup: 90 + 10 = 100 100 + 7 = 107 The pattern still works, but we create a new hundred

Guided Practice

Work together: 156 + 30 Break it down: 156 + 10 + 10 + 10 Or think: 150 + 30 = 180, then add the 6 Your turn: 234 + 40, 378 + 50

Independent Challenge

{"left":"Core Activity: Add multiples of 10 to 3-digit numbers\nSupport: Use place value charts and base-10 blocks","right":"Extension: Try adding multiples of 100\nChallenge: Can you add 90 to 3-digit numbers?"}