🧮 Adding and Subtracting Two-Digit Numbers

What you’ll learn

1. Tens and OnesSee two-digit numbers as tens and ones, like 34 = 3 tens + 4 ones.Two-digit numbers are made of tens and ones. In 34, the 3 sits in the tens place and means 30, while the 4 means just 4. Base-ten blocks show it: rods are tens and cubes are ones. Reading the places is the key that unlocks all two-digit math.
2. Adding and Subtracting TensAdd and subtract round tens mentally, like 45 + 30 = 75 and 82 − 40 = 42.Adding or subtracting tens only changes the tens digit — the ones stay put. For 45 + 30, jump up by tens: 55, 65, 75. For 82 − 40, jump back: 72, 62, 52, 42. With ten-jumps you can do two-digit math entirely in your head.
3. Three Numbers, Find the TenAdd three one-digit numbers by finding a pair that makes 10 first, like 5 + 7 + 3 = 15.To add three numbers, hunt for two that make 10. In 5 + 7 + 3, the pair is 7 + 3 = 10, and then 5 + 10 = 15. This works because numbers can be added in any order and the total never changes. Grab the easy pair first!
4. Adding Two-Digit NumbersAdd two two-digit numbers by splitting into tens and ones, like 34 + 27 = 61.To add 34 + 27, split both numbers: tens with tens (30 + 20 = 50) and ones with ones (4 + 7 = 11). Then combine: 50 + 11 = 61. When the ones make more than 9, ten of them bundle into a new ten — that is regrouping.
5. Subtracting Two-Digit NumbersSubtract two two-digit numbers using number-line jumps, like 63 − 28 = 35, and check by adding.For 63 − 28, jump back in pieces on the number line: back 20 lands on 43, then back 8 lands on 35. Always check by adding the answer back: 35 + 28 = 63, so the answer is right. Choosing the best trick — ten-jumps or splitting — makes you a two-digit champion.

Questions this course answers

Grounded in trusted sources

• Khan Academy Kids
• PBS Kids — early math
• NAEYC — early math learning
• Britannica Kids

Every Wunder lesson is built from real, reputable sources — never invented.

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