Ahava~Love Assembly

Grade 2 Mathematics Week 7 | Teacher Guide

Grade 2 | MATHEMATICS

WEEK 7 • TEACHER GUIDE AND ANSWER KEY • DAYS 31–35

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 35, read aloud if needed but give no hints.

Week 7 Student Textbook | Week 7 Practice Workbook | Week 7 Teacher Guide | Week 6 Student Textbook | Week 8 Student Textbook | Grade 2 index

Day 31: Subtract and Trade a Ten

Standard: Grade 2 Math Standard 12, 2.NBT.B.12; Grade 2 Math Standard 12, 2.NBT.B.12a

Worked example: Find 352 – 128. Worked answer: 352 – 128 = 224.

  1. 336.
  2. 325.
  3. 556 (10 – 4 = 6 after trading a ten).
  4. 324 books.
  5. There are only 4 ones, and 8 ones must be taken away, so she traded 1 ten for 10 ones to make 14 ones. 14 – 8 = 6, 4 – 1 = 3, 2 – 1 = 1, so the answer is 136. Accept any answer that says there were not enough ones.

Teaching note: Have the child build the first number with base-ten blocks and physically trade a ten rod for 10 unit cubes.

Day 32: Subtract and Trade a Hundred

Standard: Grade 2 Math Standard 12, 2.NBT.B.12; Grade 2 Math Standard 12, 2.NBT.B.12a

Worked example: Find 425 – 182. Worked answer: 425 – 182 = 243.

  1. 364.
  2. 155.
  3. 253.
  4. 273 people.
  5. The tens place. There are 6 tens, and 7 tens must be taken away, so trade 1 hundred for 10 tens to make 16 tens. 5 – 2 = 3 ones, 16 – 7 = 9 tens, 2 – 1 = 1 hundred, so the answer is 193. Accept any answer that names the tens place with a reason.

Teaching note: Ask the child to say, before subtracting, which places need a trade. This habit prevents most errors.

Day 33: Trade Two Times

Standard: Grade 2 Math Standard 12, 2.NBT.B.12; Grade 2 Math Standard 12, 2.NBT.B.12a; Grade 2 Math Standard 14, 2.NBT.B.14

Worked example: Find 531 – 276. Worked answer: 531 – 276 = 255.

  1. 284.
  2. 256.
  3. 576.
  4. 277 eggs.
  5. He took 2 from 5 and 1 from 8 instead of taking the bottom number away from the top number. He needed to trade a ten for the ones and a hundred for the tens. 12 – 5 = 7, 10 – 8 = 2, 3 – 1 = 2, so the correct answer is 227. Accept any answer that explains the trades and gives 227.

Teaching note: Noah’s error is the most common subtraction mistake. Have the child check the answer by adding: 227 + 185 = 412.

Day 34: Subtract Across Zeros and Check

Standard: Grade 2 Math Standard 12, 2.NBT.B.12; Grade 2 Math Standard 14, 2.NBT.B.14

Worked example: Find 400 – 158, then check. Worked answer: 400 – 158 = 242. The check 242 + 158 = 400 shows it is correct.

  1. 176.
  2. 236.
  3. 355.
  4. 287 + 315 = 602, so Mia is correct.
  5. 237 tickets. Check by adding 237 + 563. The sum is 800, the number of tickets the store started with, so 237 is correct. Accept 237 with any addition check that equals 800.

Teaching note: Use base-ten blocks for the first zero problem. Trading through a zero is easier to understand with blocks than with marks on paper.

Day 35: Independent Check: Subtract Within 1000

Standard: Grade 2 Math Standard 12, 2.NBT.B.12; Grade 2 Math Standard 12, 2.NBT.B.12a; Grade 2 Math Standard 14, 2.NBT.B.14

Worked example: Find 342 – 119. Worked answer: 342 – 119 = 223.

  1. 315.
  2. 338.
  3. 325.
  4. Yes. 283 + 168 = 451.
  5. 427 pencils. There were no tens, so I traded 1 hundred for 10 tens, then 1 ten for 10 ones, giving 8 hundreds, 9 tens and 15 ones. 15 – 8 = 7, 9 – 7 = 2, 8 – 4 = 4. Accept 427 with an explanation of trading through the zero.

Teaching note: Independent check: read aloud if needed, but do not help with the answers. Question 5 trades through a zero.

Week 7 Student Textbook | Week 7 Practice Workbook | Week 7 Teacher Guide | Week 6 Student Textbook | Week 8 Student Textbook | Grade 2 index