Addition to 20 Games for Kids

How the Addition to 20 Games Work

Every action in a MathHero adventure is an addition fact to solve. The sums up to 20 come in two kinds:

• Crossing 10: two one-digit numbers that add up to 11-18, like 8 + 5 and 9 + 7. These are the 36 highlighted facts in the addition chart below.
• Without crossing 10: sums that stay inside a ten, like 4 + 5, 10 + 6 and 13 + 4. Sums that land exactly on 10 or 20, like 7 + 3 and 14 + 6, count here too: they fill the ten but do not go past it.

Before the first level, each game opens a “Choose your facts” screen with two choices side by side. “With crossing 10”, picked to begin with, plays all 190 sums, and the two kinds come about equally often, so the 36 facts that cross 10 are not lost among the 154 others. “Without crossing 10” plays only the 154, for a child who is not ready to cross 10 yet. The pick is remembered for the other adventures on this page and for your next visit.

No level gets harder over time: every level draws from the facts you picked. Your child taps one of four answers, and every right answer moves the adventure forward.

MathHero has no video lessons. It builds the skill through practice, so the games work best once your child can add within 10, for example by counting on. For a guided path, the “Addition to 20” learning program in the MathHero app adds new facts a little at a time.

How to Learn Addition Facts to 20

To learn addition facts to 20, build them from the facts within 10 that your child already knows, use a strategy for the rest, then practice a little most days until the answers come from memory. Facts like 13 + 4 follow straight from a fact within 10. The real work is the 36 facts that cross 10, like 8 + 5 and 7 + 6, and three strategies cover them: make a ten, doubles, and adding 9 as 10 minus 1.

Make a ten

Fill up the bigger number to 10, then add what is left. For 8 + 5, the 8 needs 2 more to make 10, so split the 5 into 2 and 3: 8 + 2 + 3 = 10 + 3 = 13. In the same way, 7 + 6 = 7 + 3 + 3 = 13. This works for every fact that crosses 10, but only once the pairs that make 10, like 8 + 2 and 7 + 3, come quickly. Our making 10 games practice each step, and the number bonds games practice the pairs.

Doubles and near doubles

Doubles, like 6 + 6 = 12 and 8 + 8 = 16, are easy for most children to remember. A near double is a double plus one: 6 + 7 = 6 + 6 + 1 = 13, and 8 + 9 = 8 + 8 + 1 = 17. Your child can also start from the bigger double and take one away: 7 + 6 = 7 + 7 − 1 = 13.

Add 9 as 10 minus 1

Adding 10 is easy: 10 + 7 = 17. Since 9 is one less than 10, 9 + 7 is one less than 10 + 7: 17 − 1 = 16. It works with the 9 second too: 5 + 9 is 5 + 10 − 1, so 15 − 1 = 14. Spot the pattern: in every +9 fact that crosses 10, the ones digit of the answer is one less than the other number, as in 9 + 6 = 15.

Teen numbers: add the ones

In 13 + 4, the ten in 13 stays where it is. Add the ones, 3 + 4 = 7, and keep the ten: 10 + 7 = 17. So a child who knows 3 + 4 also knows 13 + 4, and 2 + 15 works the same way: 2 + 5 = 7, so 17. This is the first step toward 2-digit addition, where tens and ones are added separately.

Common mistakes

• One off when counting on. 12 for 8 + 5 usually means your child counted the 8 itself: “8, 9, 10, 11, 12”. Counting on starts from the next number: 9, 10, 11, 12, 13. Making a ten avoids the count: 8 + 2 = 10, and 3 more is 13.
• Right answer, slow way. A child who counts on fingers for every fact gets 9 + 7 right, but slowly, and the counting gets in the way once the numbers grow, as in 2-digit addition. If your child still counts most facts, practice make a ten and doubles until the answers come from memory.

For how schools teach these strategies today, see number bonds and making ten in our guide to new math.

What Grade Learns Addition to 20?

Addition within 20 is a 1st and 2nd grade skill in the US, usually learned at ages 6-8. Common Core standard 1.OA.C.6 asks 1st graders to add and subtract within 20, fluently within 10, with strategies like counting on, making ten and using doubles. Standard 2.OA.B.2 asks 2nd graders to add and subtract within 20 fluently using mental strategies, and by the end of grade 2 to know all sums of two one-digit numbers from memory. In England, Year 1 children represent and use number bonds within 20 and add one-digit and two-digit numbers to 20, and Year 2 children recall and use addition facts to 20 fluently.

Age

6-8

US grade

Grades 1-2

Standard

Common Core 1.OA.C.6, 2.OA.B.2

England

Years 1-2