NCERT Revision Notes for Class 3 Maths Chapter 9: House of Hundreds – II – Free PDF Download

Chapter 9 of Class 3 Maths, House of Hundreds – II, continues building on three-digit number understanding from Chapter 6, focusing this time on adding and subtracting three-digit numbers, including regrouping across hundreds, tens, and ones.

Last Updated: September 23, 2026

Key Concepts

Adding three-digit numbers: adding hundreds to hundreds, tens to tens, and ones to ones, with regrouping when a column adds up to 10 or more.

Subtracting three-digit numbers: subtracting hundreds, tens, and ones, with borrowing across columns when needed.

Regrouping across two columns: sometimes borrowing is needed from the hundreds place all the way through the tens place to the ones place.

Estimating sums and differences: rounding numbers to the nearest ten or hundred to quickly estimate an answer before calculating exactly.

Word problems with three-digit numbers: real-life situations, like combining or comparing larger quantities, written as addition or subtraction number sentences.

Worked Examples

Example 1

Add 356 + 278. Ones: 6 + 8 = 14, write 4 carry 1. Tens: 5 + 7 + 1 = 13, write 3 carry 1. Hundreds: 3 + 2 + 1 = 6. So 356 + 278 = 634.

Example 2

Subtract 500 − 236. Since borrowing is needed across two columns, 500 − 236 = 264.

Example 3

Estimate 298 + 405 by rounding to the nearest hundred. 298 rounds to 300, and 405 rounds to 400, so the estimated sum is about 700; the exact answer, 703, is close to this estimate.

Quick Recap

• Adding and subtracting three-digit numbers follows the same column method as two-digit numbers, with an extra hundreds column.
• Regrouping may be needed in the ones, tens, or even across both columns.
• Estimating by rounding helps check whether an exact answer seems reasonable.
• Word problems involving larger quantities are solved using the same addition and subtraction methods.
• Practising with numbers like 500, which need regrouping across two places, builds strong subtraction skills.

Common Mistakes to Avoid

• Forgetting to carry or borrow correctly when regrouping across more than one column.
• Misaligning hundreds, tens, and ones columns while writing the sum or difference.
• Making an error when subtracting from a number with zeros, like 500 or 600.
• Rounding numbers incorrectly while estimating, leading to a very inaccurate check.
• Using the wrong operation in a word problem due to not reading it carefully.

Home Practice Tips

• Practise a few three-digit addition and subtraction sums daily, including some with numbers like 300, 500, or 800.
• Use place value blocks to show regrouping across hundreds, tens, and ones.
• Practise estimating answers by rounding before solving a sum exactly.
• Create simple three-digit word problems together using real-life quantities, like money saved or distances.
• Check subtraction answers by adding the answer back to the number subtracted.

Frequently Asked Questions

Q1. What makes subtracting from numbers like 500 or 600 tricky?
These numbers have zeros in the tens and ones places, so borrowing must happen across two columns at once, which needs extra care and practice.

Q2. How can I help my child avoid regrouping mistakes?
Use place value blocks to physically show carrying and borrowing, and encourage the child to write carried or borrowed numbers clearly above the columns.

Q3. Why is estimating useful before solving an exact sum?
Estimating by rounding gives a quick, approximate answer that helps check whether the final exact answer is reasonable or likely has a mistake.

Q4. What kind of word problems appear in this chapter?
Word problems combining or comparing three-digit quantities, such as adding collected items over two days or finding the difference between two larger amounts.

Q5. How does this chapter connect to Chapter 6, House of Hundreds – I?
It builds directly on the place value understanding from Chapter 6, applying it to actually add and subtract three-digit numbers with regrouping.

Full walkthrough: Chapter 9 Solutions for step-by-step textbook answers.

Written by Satish

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