Math Expressions Grade 2, Unit 6: 3-Digit Addition and Subtraction
In this unit, your child adds and subtracts three-digit numbers within 1,000. They count and skip-count by 5s, 10s, and 100s, read each digit's place value, add or subtract 10 and 100 in their heads, and explain how they regroup. This builds on time, graphs, and word problems and leads into arrays and equal shares.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
What is my child learning in Unit 6?
- Reading three-digit numbers as hundreds, tens, and ones, including numbers with a zero, like 706. Learn more: Hundreds, tens, and ones in numbers like 706
- Counting within 1,000 and skip-counting by 5s, 10s, and 100s, starting from numbers like 245. Learn more about counting within 1,000: Counting within 1,000 · Learn more about skip-counting by 5s, 10s, and 100s
- Adding and subtracting within 1,000, regrouping ones, tens, and hundreds, as in 365 + 248 = 613. Learn more about adding within 1,000: Adding within 1,000 · Learn more about subtracting within 1,000
- Adding or subtracting 10 or 100 in their heads, such as finding that 100 less than 527 is 427. Learn more: Adding or taking away 10 or 100 mentally
- Explaining how place value makes each step work, such as why 1 hundred can become 10 tens. Learn more about explaining why addition strategies work: Explaining why addition strategies work · Learn more about explaining why subtraction strategies work
Sample questions to try together
These are real questions from our practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
How many hundreds are in 300?
- 3
- 30
- 300
How you can help
- Count by 100s starting at 245 on a walk or ride, then switch to 10s. Ask your child what comes after 295 when counting by 10s.
- Ask for 100 less and 10 less than a house number or price you see, like 527. Then ask which digit changed each time.
- Let your child be the teacher: ask them to explain how they solved 365 + 248, using hundreds, tens, and ones in their own words.
Where kids can get stuck
- Writing 76 for seven hundred six because the zero seems to mean nothing.
- Stumbling over a new hundred, going from 199 to 1000 instead of 200.
- Subtracting the smaller digit from the larger in each place, so 402 - 175 becomes 373.
Practice makes perfect
Bobby's Math Club has practice problems that adapt to your child’s level, each with a detailed explanation and an easy-to-follow video, so your child can build confidence in these skills one step at a time.
Words your child will hear
- hundred
- Ten tens, or 100. The 7 in 706 means 7 hundreds.
- digit
- One of the symbols 0 to 9 used to write numbers. 352 has three digits.
- place value
- What a digit is worth because of where it sits. In 352, the 5 means 50.
- skip-count
- To count by a number other than 1, such as 5, 10, 15, 20.
- regroup
- To trade 10 ones for 1 ten, or 10 tens for 1 hundred, and back again.
- decompose
- To break a number into parts, like 82 = 80 + 2, or 1 hundred into 10 tens.
- mentally
- In your head, without writing it down.
Ready to build your child’s confidence with adding and subtracting to 1,000?
In Bobby's Math Club, your child practices these skills at just the right level, with a hint when they need one, a clear explanation after every question, and kid-friendly videos. Unlimited practice is free.
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Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
Which math standards does Math Expressions Grade 2 Unit 6 cover?
Math Expressions Grade 2 Unit 6 covers these math standards. Each one links to what it means, sample questions, and teaching strategies.
- 2.NBT.A.1: Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones.
- 2.NBT.A.2: Count within 1000; skip-count by 5s, 10s, and 100s.
- 2.NBT.B.7: Add and subtract within 1000.
- 2.NBT.B.8: Mentally add 10 or 100 to a given number 100–900.
- 2.NBT.B.9: Explain why addition and subtraction strategies work.
For teachers: Unit names and order vary between editions and districts, so your school’s own materials have the exact sequence. Learn how Bobby's Math Club can help your students grow.