Mathematics
Remember?
3 quick questions from earlier weeks · about 3 minutes
- 4 + 6 = ? Facts to 20
- What is 100 more than 782? Week 10
- 11 + 16 + 20 = ? Week 8
Objective: Students explain why the make-a-ten and decomposition strategies work using place value language and drawings (2.NBT.B.9).
- 10 min — Warm-Up: Spiral from Week 10: say 10 more and 100 less for 462 and 807 (472 and 362, 817 and 707). Then ask your child to solve 38 + 47 any way they like and tell you every step aloud (85).
- 15 min — Mini-Lesson: Write 38 + 47 = 85 and ask the week's big question: 'Why does that work?' Model an explanation with straws: '38 is 3 tens and 8 ones. 47 is 4 tens and 7 ones. Tens go with tens: 7 tens. Ones go with ones: 15, which is 1 ten and 5 ones. That makes 8 tens and 5 ones.' Write it as 30 + 40 = 70, 8 + 7 = 15, 70 + 15 = 85. Say, 'This is called decomposing, breaking numbers into their place value parts.'
- 15 min — Practice: Your child solves 56 + 29 and 43 + 38 by decomposing (85, 81), writing the three lines each time (tens sum, ones sum, total). Then they write 2 sentences under each explaining why splitting the numbers into tens and ones does not change the answer.
- 5 min — Wrap-Up: Ask, 'If you split 56 into 50 and 6, do you still have 56? How do you know?' Have your child prove it with 5 bundles and 6 straws.
Materials: paper, pencil, straws bundled by ten, loose straws