Ahava~Love Assembly

Grade 2 Mathematics Week 5 | Teacher Guide

Grade 2 | MATHEMATICS

WEEK 5 • TEACHER GUIDE AND ANSWER KEY • DAYS 21–25

Read each lesson aloud with the child and model the worked example before practice. Do not show this key during practice. Accept oral, drawn or written answers where the child cannot yet write the whole answer. On Day 25, read aloud if needed but give no hints.

Week 5 Student Textbook | Week 5 Practice Workbook | Week 5 Teacher Guide | Week 4 Student Textbook | Week 6 Student Textbook | Grade 2 index

Day 21: Add Three Two-Digit Numbers

Standard: Grade 2 Math Standard 11, 2.NBT.B.11

Worked example: Add 21 + 35 + 12. Worked answer: 21 + 35 + 12 = 68.

  1. 67.
  2. 78.
  3. 68.
  4. 66.
  5. Each number is made of tens and ones. Adding all the tens and all the ones counts every part of every number once, so the total is the same. Accept any answer about counting every ten and every one.

Teaching note: Today’s problems need no regrouping. Regrouping comes on Day 22.

Day 22: When the Ones Make a New Ten

Standard: Grade 2 Math Standard 11, 2.NBT.B.11; Grade 2 Math Standard 14, 2.NBT.B.14

Worked example: Add 37 + 24 + 13. Worked answer: 37 + 24 + 13 = 74.

  1. 55.
  2. 86.
  3. 87.
  4. 8 and 2 (from 18 and 22).
  5. 15 ones is the same as 1 ten and 5 ones. The 1 ten is added to the other tens and the 5 ones stay in the ones place. Accept any answer that trades ten ones for one ten.

Teaching note: Use base-ten blocks and physically trade ten ones for a ten. Ask the child to say why the trade does not change the amount.

Day 23: Add Four Two-Digit Numbers

Standard: Grade 2 Math Standard 11, 2.NBT.B.11

Worked example: Add 12 + 30 + 18 + 21. Worked answer: 12 + 30 + 18 + 21 = 81.

  1. 69.
  2. 73.
  3. 80.
  4. 70.
  5. Changing the order or grouping does not add or remove any berries, blocks or numbers. Every number is still counted once, so the total stays the same. Accept any answer about counting the same amounts.

Teaching note: Encourage the child to find friendly pairs that make tens before adding.

Day 24: Explain Your Strategy

Standard: Grade 2 Math Standard 14, 2.NBT.B.14

Worked example: Explain why 38 + 25 = 63 using tens and ones. Worked answer: The tens make 50, and the ones make 13, which is one more ten and 3 ones. So the total is 63.

  1. 72 (40 + 20 = 60, 5 + 7 = 12, 60 + 12 = 72).
  2. 85 (56 + 4 = 60, 60 + 25 = 85).
  3. 52.
  4. One possible mistake is that Leo did not regroup the new ten: 4 + 8 = 12, but he kept only the 2 ones and lost the ten, getting 42. Accept any mistake that would lead to 42 and is explained clearly.
  5. Ten ones and one ten are the same amount, so trading one for the other changes how we write the number, not how much there is. Accept any answer that says ten ones equal one ten.

Teaching note: Ask the child to explain aloud before writing. Accept other correct strategies that keep every amount.

Day 25: Independent Check: Adding Many Numbers

Standard: Grade 2 Math Standard 11, 2.NBT.B.11; Grade 2 Math Standard 14, 2.NBT.B.14

Practice record: Reading log, printed on the Week 5 Practice Workbook.

Worked example: Add 16 + 22 + 31. Worked answer: 16 + 22 + 31 = 69.

  1. 77.
  2. 90.
  3. 75.
  4. Ana’s 26 and Cal’s 34 make 60, or Ben’s 17 and Dee’s 13 make 30. The ones make a ten. Accept any pair whose ones make 10.
  5. Accept any correct method that adds every number once, such as tens 20 + 10 + 30 + 10 = 70 and ones 6 + 7 + 4 + 3 = 20, so 70 + 20 = 90, or pairing 26 + 34 = 60 and 17 + 13 = 30.

Teaching note: Independent check: read aloud if needed, but do not help with the answers.

Week 5 Student Textbook | Week 5 Practice Workbook | Week 5 Teacher Guide | Week 4 Student Textbook | Week 6 Student Textbook | Grade 2 index