Cogito
Grade 2 Math · Chapter 3 · Lesson 9
Ten More, Ten Less
Add or take a ten without counting.
10 problems · about 12 minutes · 2.NBT.B.8
What this lesson teaches
The child mentally adds and subtracts 10 from any number between 100 and 900.
- Ten more changes only the tens digit.
- Unless the tens are full, and then a hundred is made.
- You can do this in your head.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Using Greater Than and Less Than: Which symbol makes this true: 415 ? 451
Answer <
Why 415 is less than 451.
Review — Comparing Three-Digit Numbers: Which is greater, 548 or 584?
Answer 584
Why 8 tens beats 4 tens.
Warm Up
Straightforward practice. Get the method working first.
4 problemsTen more than 236 is?
Answer 246
Why 236 + 10 = 246.
Ten more than 390 is?
Answer 400
Why 390 + 10 = 400.
Ten more than 315 is?
Answer 325
Why The 3 and the 5 stay.
Ten less than 682 is?
Answer 672
Why Take one ten off.
Build It Up
The same ideas with more to keep track of.
2 problemsTen more than 495 is?
Answer 505
Why Nine tens and one more ten.
Ten less than 703 is?
Answer 693
Why There are no tens to take, so unbundle a hundred.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Collection: Leo has 428 stamps and buys 10 more. How many now?
Answer 438 stamps
Why 428 + 10 = 438.
Giving Some Away: Ana has 561 beads and gives away 10. How many are left?
Answer 551 beads
Why 561 − 10 = 551.