Cogito
Grade 1 Math · Chapter 7 · Lesson 7
Ten More, Ten Less
Add or take ten without counting one by one.
10 problems · about 12 minutes · 1.NBT.C.5
What this lesson teaches
The child finds ten more and ten less than a two-digit number mentally, and explains why only the tens digit changes.
- Ten more is the square straight below.
- Ten less is the square straight above.
- Only the tens digit changes.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — 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.
Review — Many Ways to Show a Number: 2 tens and 16 ones is which number?
Answer 36
Why 20 and 16 is 36.
Review — Multiples of Ten: Three tens is which number?
Answer 30
Why Three tens is 30.
Warm Up
Straightforward practice. Get the method working first.
3 problemsWhat is ten more than 21?
Answer 31
Why 2 tens became 3 tens.
Which digit changes when you add ten?
Answer The tens digit.
Why You added one more ten, so only the tens changed.
What is ten more than 14?
Answer 24
Why Move straight down.
Build It Up
The same ideas with more to keep track of.
1 problemWhat is ten less than 36?
Answer 26
Why Move straight up.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsWhat is ten more than 30?
Answer 40
Why 3 tens and one more ten.
A Bag of Marbles: Leo has 27 marbles. He wins ten more. How many now?
Answer 37 marbles
Why 2 tens became 3 tens, so 27 became 37.