When you adjust you make a small change to a number. This is done to make a calculation easier to solve mentally.

The inverse is the opposite or reverse operation. For example, subtraction is the inverse operation of addition.

Working efficiently means finding a way to solve a problem quickly whilst also maintaining accuracy.

Add two 3-digit numbers using adjusting strategies

Maths

In this unit pupils will add and subtract two 3-digit numbers using partitioning, adjusting, redistribution and bridging. In the future unit pupils will accurately and efficiently solve multi-step addition and subtraction problems. They will understand and explain how both addition and subtraction equations can be used to describe the same additive relationship.

In the prior unit pupils found pairs of number that composed 100 and positioned 3-digit numbers on a number line and estimated their position on unmarked number lines. They compared and ordered 3 digit numbers. In this unit pupils will add and subtract two 3-digit numbers using partitioning, adjusting, redistribution and bridging

Informal and mental strategies for adding and subtracting two 3-digit numbers

Which of these number line represents using adjustment to find the total of 25 + 49?

Solve the following sum using adjustment. 360 + 499 = {{ }}

Solve the following sum using adjustment. {{ }} = 390 + 270

Solve the following sum by adjusting both addends. {{ }} = 199 + 599 

Solve the following sum using adjustment. 397 + 296 = {{ }}

Which of these numbers is closest to a tens boundary?

Which of these numbers is closest to 100?

Which number is closest to a hundreds boundary?

Which of these number lines accurately represents 22 + 12 = 34 using partitioning to bridge?

This lesson will soon be taken down.

Add two 3-digit numbers using adjusting strategies

Lesson outcome