Adding whole tens (3 addends) (211)

Teaching Notes

Teach students to add in pairs: combine first two tens, then add the third. Emphasize counting by tens (30, 50, 90). Model thinking aloud: "I have 3 tens and 2 tens, that's 5 tens or 50. Then add 4 more tens to get 9 tens or 90."

Vocabulary

Addend: A number that is added.

Sum: The total when numbers are added.

Common Mistakes

• Adding ones place instead of tens
• Forgetting to add all three numbers
• Losing track of which numbers were already added
• Writing 3+2+4=9 instead of 90
• Forgetting to include the zero in the sum (e.g., 20+30+40=9 instead of 90).
• Miscounting when summing the 'tens' digits if done mentally.
• Difficulty tracking multiple addends without visual aids.

Differentiation

Discussion Questions

• How is adding 20 + 30 + 40 similar to adding 2 + 3 + 4?
• Why is it important to know how to add whole tens quickly?
• Can you think of a real-life situation where you might add three groups of tens?

Extension Activities

• Use a calculator to check sums.
• Create word problems with three addends.
• Practice adding in reverse order.

Parent Tip

Have your child add three small groups of objects together.

Skill Cluster

Number Sense & Operations: Addition

Estimated Time

15 minutes

Skills Practiced

Prerequisites

• Adding three single-digit numbers
• Adding two multiples of ten
• Place value to 100

Next Steps

• Adding three 2-digit numbers (without regrouping)
• Adding three 2-digit numbers (with regrouping)
• Adding three multiples of one hundred