Cogito
Grade 1 Math · Chapter 8 · Lesson 1
Adding Tens to Tens
Add whole tens the same way you add ones.
10 problems · about 10 minutes · 1.NBT.C.4
What this lesson teaches
The child adds multiples of ten within 40 by treating a ten as a unit, recognizing 3 tens + 1 ten as parallel to 3 + 1.
- A ten is something you can count.
- 3 tens and 1 ten is 4 tens.
- 30 + 10 = 40.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — One More, One Less, Ten More, Ten Less: Ten less than 34 is?
Answer 24
Why 3 tens became 2 tens.
Review — Ten More, Ten Less: What is ten more than 21?
Answer 31
Why 2 tens became 3 tens.
Review — Greater Than, Less Than, Equal To: What does < mean?
Answer Is less than.
Why < means is less than.
Review — Which Is More?: Which is greater, 30 or 27?
Answer 30
Why 30 has 3 tens. 27 has 2 tens.
Warm Up
Straightforward practice. Get the method working first.
3 problems20 + 10 = ?
Answer 30
Why 2 tens and 1 ten is 3 tens.
10 + 30 = ?
Answer 40
Why Four tens is 40.
10 + 10 = ?
Answer 20
Why 1 ten and 1 ten.
Build It Up
The same ideas with more to keep track of.
1 problem20 + 20 = ?
Answer 40
Why 2 tens and 2 tens.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems30 + 10 = ?
Answer 40
Why 3 tens and 1 ten.
Two Boxes: Leo has 20 crayons. He gets a box of 10 more. How many?
Answer 30 crayons
Why 20 + 10 = 30.