42 − 17
Trade one ten: 42 becomes 3 tens and 12 ones. Ones: 12 − 7 = 5. Tens: 3 − 1 = 2.
Answer: 42 − 17 = 25 25 + 17 = 42, which checks the subtraction.
Subtraction · Grades 2–4
How to Subtract with Regrouping
Regrouping lets us rename a number using equal place-value amounts. When a column has too few to subtract, trade from the next place.
What children need to know first
- A ten is equal to ten ones; one hundred is equal to ten tens.
- Digits in the same column represent the same place value.
Step-by-step explanation
- Write the numbers so ones, tens, and hundreds line up.
- Start in the ones column. If the top digit is too small, regroup one ten as ten ones.
- Subtract the ones, then move left to the tens and hundreds.
- Check by adding the difference and the number subtracted.
Worked examples
63 − 28
Trade one ten: 63 becomes 5 tens and 13 ones. Ones: 13 − 8 = 5. Tens: 5 − 2 = 3.
Answer: 63 − 28 = 35 35 + 28 = 63, so the difference is correct.
Common mistakes and how to fix them
- Changing the ones but forgetting to reduce the tens. Show the trade with base-ten blocks or a crossed-out digit.
- Subtracting the smaller digit from the larger in each column regardless of position. Regroup when needed instead.
Parent teaching tips
- Build the minuend with tens rods and ones cubes so the trade is visible.
- Ask the child to name the value before and after regrouping; it remains 42.
Independent practice
- Solve 51 − 26.
- Solve 74 − 38.
Practice answers
- 25
- 36
Explore related skills
Practice this skill
Open the matching Grades 2–4 activity for Subtraction. You can print its worksheet with questions only or an answer key.
Start Subtraction practice · View the grade-level topic page