💯 Adding and Subtracting Within 100

What you’ll learn

1. Fast Facts to 10Quickly recall addition and subtraction facts within 10, especially the pairs that make 10.Small facts are the building blocks of all bigger math. Pairs like 6 and 4 or 7 and 3 snap together to make 10, and knowing them helps subtraction too, like 9 − 4 = 5. The faster these facts come to mind, the easier every later strategy becomes.
2. Making Ten to AddAdd within 20 by breaking one number apart to make a ten first, like 8 + 6 = 8 + 2 + 4 = 14.Ten is the friendliest number to add to, so we turn hard sums into a ten plus extra. For 8 + 6, give 8 the 2 it needs to become 10, then add the leftover 4 to get 14. The same trick solves 9 + 5: 9 + 1 = 10, then 10 + 4 = 14.
3. Breaking Apart to SubtractSubtract within 20 by splitting the number being taken away so you stop at 10, like 13 − 4 = 13 − 3 − 1 = 9.Big take-aways become easy when you rest at 10 on the way. For 13 − 4, hop back 3 to land on 10, then 1 more to land on 9. Splitting the small number, like 7 into 5 and 2 for 15 − 7, makes every subtraction just two friendly hops.
4. Adding TensAdd or subtract a whole number of tens from a two-digit number, like 38 + 40 = 78.Whole tens are big, easy jumps. In 38 + 40, the 3 tens become 7 tens while the 8 ones never move, giving 78. Subtracting tens works the same way: 86 − 20 = 66. Only the tens digit changes when you add or take away whole tens.
5. Big Number Plus Small NumberAdd a one-digit number to a two-digit number by bridging through the next ten, like 46 + 7 = 46 + 4 + 3 = 53.To add a small number to a big one, jump to the next ten first. 46 needs 4 to reach 50, so split 7 into 4 and 3: 46 + 4 = 50, then 50 + 3 = 53. Crossing the ten makes the tens digit grow, and the same move works for any sum, like 58 + 6 = 64.

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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