2.3 Mental Strategies for Subtraction

Unit Objectives

• We are learning to explore and choose appropriate mental subtraction strategies such as the compensation strategy and rounding to solve subtraction problems.

Success Criteria

• I can round numbers and use the compensation strategy to solve subtraction problems.

• I can use rounding to check answers and count on to solve subtraction problems.

• I can use subtraction strategies to solve word problems.

Learning Objective

• To use compensation of an addend to solve subtraction problems. 

Success Criteria

• I can round the addend to the nearest 10.

• I can subtract using the 10's number.

• I can compensate to solve the equation.

Compensate: to make up for something lost,
missing, or broken, or to pay someone for their work.

Follow along to write notes to help you remember what you've learned.

Learning Objective

• To use compensation of an addend to solve subtraction problems. 

Success Criteria

• I can round the addend to the nearest 10.

• I can subtract using the 10's number.

• I can compensate to solve the equation.

Let's review how to use the compensation strategy to solve equations.

Aim: Complete page 36 ONLY.

Learning Objective

• To use rounding to check if our mental subtraction answers are reasonable.

Success Criteria

• I can round the numbers.

• I can subtract using the rounded numbers.

• I can check if my answer makes sense.

• I can fix my answer if needed.

Rounding helps us estimate, not get the exact answer —
it helps us check if our thinking is reasonable.

Worked Example

363-198

🎯 Step One: Round the subtrahend

🎯 Step Two: Do the simpler math

🎯 Your answer should be close to?

Estimate the subtrahend for the following using rouding.

Now solve both equations using compensation.

Aim: Complete page 37 ONLY.