Grade 2 | MATHEMATICS
WEEK 6 • STUDENT TEXTBOOK • DAYS 26–30
Read each lesson with a parent or teacher and study the worked example. Then answer the questions for that day in the Week 6 Practice Workbook.
Week 6 Student Textbook | Week 6 Practice Workbook | Week 6 Teacher Guide | Week 5 Student Textbook | Grade 2 index
Day 26: Add or Subtract 10 in Your Head
When you add 10, the tens digit goes up by one and the ones digit stays the same. When you subtract 10, the tens digit goes down by one.
Start with 345. Add 10: 355. Subtract 10: 335. If the tens digit is 9 and you add 10, the hundreds go up: 390 + 10 = 400.
Worked example: What is 472 + 10?
- The tens digit is 7.
- Adding 10 makes it 8.
- The hundreds and ones stay the same.
Worked answer: 472 + 10 = 482.
Day 27: Add or Subtract 100 in Your Head
When you add 100, the hundreds digit goes up by one. When you subtract 100, the hundreds digit goes down by one. The tens and ones stay the same.
Start with 528. Add 100: 628. Subtract 100: 428.
Worked example: What is 836 – 100?
- The hundreds digit is 8.
- Subtracting 100 makes it 7.
- The tens and ones stay the same.
Worked answer: 836 – 100 = 736.
Day 28: Add Three-Digit Numbers with Models
To add three-digit numbers, add hundreds to hundreds, tens to tens and ones to ones.
Draw squares for hundreds, sticks for tens and dots for ones, or use base-ten blocks. For 213 + 154, the hundreds make 300, the tens make 60 and the ones make 7, so the total is 367.
Worked example: Add 321 + 245.
- Hundreds: 300 + 200 = 500.
- Tens: 20 + 40 = 60.
- Ones: 1 + 5 = 6.
- 500 + 60 + 6 = 566.
Worked answer: 321 + 245 = 566.
Day 29: Regroup When Adding Within 1000
If the ones add to 10 or more, trade 10 ones for 1 ten. If the tens add to 10 or more, trade 10 tens for 1 hundred. This is called composing a new ten or a new hundred.
For 356 + 278: ones 6 + 8 = 14, so trade for 1 ten and 4 ones. Tens 5 + 7 + 1 = 13, so trade for 1 hundred and 3 tens. Hundreds 3 + 2 + 1 = 6. The total is 634.
Worked example: Add 247 + 136.
- Ones: 7 + 6 = 13. Trade 10 ones for 1 ten. Keep 3 ones.
- Tens: 4 + 3 + 1 = 8.
- Hundreds: 2 + 1 = 3.
Worked answer: 247 + 136 = 383.
Day 30: Independent Check: Mental Math and Adding Within 1000
Today you will work on your own.
Add or subtract 10 and 100 in your head, and add three-digit numbers by place, trading when a place has 10 or more.
Worked example: What is 530 + 100?
- The hundreds digit is 5.
- Adding 100 makes it 6.
Worked answer: 530 + 100 = 630.
Week 6 Student Textbook | Week 6 Practice Workbook | Week 6 Teacher Guide | Week 5 Student Textbook | Grade 2 index