Mental Subtraction within 0–100 (790)

Teaching Notes

Model count-up strategy.

Vocabulary

Mental math: Calculating in your head.

Break apart: Decompose a number into parts.

Common Mistakes

• adding instead of subtracting
• Forgetting place value.
• Incorrectly applying strategies.
• Sloppy mental tracking.
• Rushing calculations.

Differentiation

Discussion Questions

• How did you solve this mentally?
• Can you think of another strategy?
• When is counting up most useful?
• Why are friendly tens helpful?

Extension Activities

• Subtract across 100.
• Subtract using number lines.
• Create subtraction stories.

Parent Tip

Use small objects to show subtracting parts of a number.

Skill Cluster

Number Sense and Operations

Estimated Time

10 minutes

Skills Practiced

Prerequisites

• Subtraction within 20
• Place Value to 100
• Mental Addition within 100 without Regrouping

Next Steps

• Mental Subtraction with Regrouping
• Estimating Differences
• Multi-Digit Subtraction
• Mental Subtraction within 0–100 - Set B
• Mental Subtraction within 0–100 with Regrouping
• Mental Addition within 0–100