1st Grade Addition Within 20 Worksheet Solutions (PDF)
This addition within 20 answers for 1st Grade covers addition within 20 (Common Core 1.OA.A.1, 1.OA.B.3, 1.OA.C.6, 1.OA.C.5), with a free PDF to print.
Here are the full answers for the addition within 20 worksheet. Each answer shows the strategy: counting on, making a ten or doubles. Check the sum, then check the strategy.
Grade 1 · Common Core State Standards: 1.OA.A.1, 1.OA.B.3, 1.OA.C.6, 1.OA.C.5
Addition within 20 answers: exercises 1 to 10
Exercise 1 – Count the counters
3 blue and 2 orange. \(3 + 2 = 5\).
The sum is 5.
Exercise 2 – Count on from the bigger number
Start at 6. Count on 2: 7, 8. \(6 + 2 = 8\).
The sum is 8.
Exercise 3 – Add the picture
\(5 + 3 = 8\).
The sum is 8.
Exercise 4 – Add zero
Adding zero changes nothing. \(9 + 0 = 9\).
The sum is 9.
Exercise 5 – Doubles fact
Both groups have 4. \(4 + 4 = 8\).
The sum is 8.
Exercise 6 – Bigger doubles
Double 7 is 14. \(7 + 7 = 14\).
The sum is 14.
Exercise 7 – Switch the order
The other order is \(8 + 3\). Start at 8 and count on 3: 9, 10, 11. \(8 + 3 = 11\) and \(3 + 8 = 11\).
The sum is 11.
Exercise 8 – Make a ten with 9
Move 1 counter to fill the first frame. That makes 10 and 3 more. \(10 + 3 = 13\).
The sum is 13.
Exercise 9 – Make a ten with 8
8 needs 2 more to make 10. Take 2 from 6, and 4 is left. \(10 + 4 = 14\). Check: \(8 + 6 = 14\).
The sum is 14.
Exercise 10 – Near doubles
\(6 + 6 = 12\). 7 is one more than 6, so add 1. \(12 + 1 = 13\).
The sum is 13.
Exercises 11 and up
Exercise 11 – Same sum
The order can change. \(7 + 5 = 5 + 7\). Both are 12.
The missing number is 7.
Exercise 12 – Count on 2
15, then 16, then 17. \(15 + 2 = 17\).
You reach 17.
Exercise 13 – Three numbers, make ten
7 and 3 make 10. \(2 + 10 = 12\). Check: \(2 + 7 = 9\), \(9 + 3 = 12\).
The sum is 12.
Exercise 14 – Three numbers, look for a pair
6 and 4 make 10. \(10 + 5 = 15\).
The sum is 15.
Exercise 15 – Compare sums
\(8 + 5 = 13\) and \(9 + 3 = 12\). 13 is more than 12.
\(8 + 5 > 9 + 3\). The symbol is >.
Exercise 16 – Sticker story
Add to the 7 stickers. \(7 + 6 = 13\).
Priya has 13 stickers.
Exercise 17 – Marbles together
Put the groups together. \(9 + 8 = 17\). (Think: \(9 + 9 = 18\), and 8 is one less than 9.)
There are 17 marbles.
Exercise 18 – Muffin doubles
Two equal groups. \(6 + 6 = 12\).
Diego bakes 12 muffins.
Exercise 19 – Pages read
8 and 2 make 10. \(10 + 6 = 16\).
Mei reads 16 pages.
Exercise 20 – Is he right?
\(9 + 5 = 14\) and \(10 + 4 = 14\). Move 1 from the 5 to the 9 to get 10 and 4.
Yes, Noah is right. Both sums are 14.
Key facts behind this addition within 20 answers
- The sum is the total. In 5 + 3 = 8, the sum is 8.
- Counting on: start at the bigger number and count up the smaller one.
- Make a ten: 8 + 5 = 10 + 3 = 13.
- Doubles help: 6 + 6 = 12, so 6 + 7 = 13.
- Order does not matter, and adding 0 leaves a number the same.
How to use this addition within 20 answers
Cover each solution, solve the exercise again, then uncover it and compare every line. If your answer differs, find the first step that changed and redo the exercise from there.
All Grade 1 chapters: Grade 1 math.
