Addition and subtraction without regrouping

This is the easier half. When the ones add up to less than ten, the rest is comfortable.

When this applies

Look at the ones in both numbers. If their sum stays at most 9, you don't need any regrouping.

• 24 + 13 → ones 4 + 3 = 7. Easy.
• 51 + 36 → ones 1 + 6 = 7. Easy.
• 42 + 5 → ones 2 + 5 = 7. Easy.

The two-step method

1. Add the ones. Look only at the right digit of each number and add them.
2. Add the tens. Look at the left digit of each number and add them.

Put the answer together: tens on the left, ones on the right.

Example: 24 + 13

• Ones: 4 + 3 = 7.
• Tens: 2 + 1 = 3.
• Together: 3 tens and 7 ones = 37.
• 24 + 13 = 37.

Example: 50 + 36

• Ones: 0 + 6 = 6.
• Tens: 5 + 3 = 8.
• 50 + 36 = 86.

What about subtraction

Subtraction works the same way. If the ones digit of the top number is at least as big as the bottom one, you don't need to regroup.

75 − 23:

• Ones: 5 − 3 = 2.
• Tens: 7 − 2 = 5.
• 75 − 23 = 52.

98 − 67:

• Ones: 8 − 7 = 1.
• Tens: 9 − 6 = 3.
• 98 − 67 = 31.

A quick check before you start

Before you compute: look at the ones. If the sum (or difference) lands in 0–9, you're on the easy path. If it lands at 10 or more (when adding) or below zero (when subtracting), you'll need regrouping — the next article shows that.

Summary

• Without regrouping = the ones fit under ten.
• Method: ones first, then tens.
• Works the same for adding and subtracting.
• Look at the ones first — saves time.