Cogito
Grade 1 Math · Chapter 10 · Lesson 6
Ten More, Ten Less to 100
Move by ten anywhere on the chart.
10 problems · about 12 minutes · 1.NBT.C.5
What this lesson teaches
The child finds ten more and ten less for any number to 100 mentally, and explains why the ones digit is unchanged.
- Ten more and ten less only change the tens digit.
- The ones digit stays exactly the same.
- This works for every number to 100.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Comparing Numbers to 100: Which is greater, 38 or 41?
Answer 41
Why 41 has more tens.
Review — Counting to 120: What comes right after 104?
Answer 105
Why After 104 comes 105.
Review — Numbers to 100: How many ones are in 86?
Answer 6
Why 86 is 8 tens and 6 ones.
Review — Two-Bar Tape Diagrams: Bars of 15 and 8. What is the difference?
Answer 7
Why 15 − 8 = 7.
Warm Up
Straightforward practice. Get the method working first.
3 problemsTen more than 66 is?
Answer 76
Why 6 tens became 7 tens.
Ten less than 41 is?
Answer 31
Why 4 tens became 3 tens.
Ten more than 35 is?
Answer 45
Why The 5 stays.
Build It Up
The same ideas with more to keep track of.
1 problemTen less than 72 is?
Answer 62
Why The 2 stays.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTen more than 90 is?
Answer 100
Why Nine tens and one more ten.
Saving Stickers: Ana has 48 stickers. She gets ten more. How many now?
Answer 58 stickers
Why 4 tens became 5 tens, so 48 became 58.