How to play Sums to 20
- A sum waits above the board, such as 13 + 5 or 17 − 9. Work out the answer.
- Tap a column to drop it next to a block with that answer. The sum and the answer disappear together.
- If it lands anywhere else, the sum turns into its answer and becomes a number block.
- The game ends when a column is full to the top.
Stuck? Press Hint to see a column where your block makes a bond. Every bond you make, the adder above the board eats it and grows one block longer.
Easy gives more blocks that fit somewhere, Tricky fewer.
For parents and teachers
Sums to 20 practises addition and subtraction within 20, including the sums that cross 10, like 8 + 7 or 15 − 8. Adding and subtracting within 20 is a grade 1 standard in the US Common Core (1.OA.C.6), and recalling these facts fluently is a Year 2 objective in England’s national curriculum.
A guide: ages 7 to 8, after Sums to 10.
The Block Adder games
- Make 5: Find two blocks that add up to 5, like 2 and 3.
- Make 10: Find two blocks that add up to 10, like 3 and 7.
- Make 20: Find two blocks that add up to 20, like 12 and 8.
- Make 100: Find two tens that add up to 100, like 30 and 70.
- Sums to 10: Drop each sum on its answer: 4 + 3 goes on a 7.
- Sums to 20: Drop each sum on its answer: 12 − 3 goes on a 9.
Questions
How can my child work out sums that cross 10?
Through 10: for 8 + 7, take 2 from the 7 to make 10, then add the 5 left over. The bonds to 10 from Make 10 are what makes this quick.
Are the answers always whole numbers?
Yes. Every answer is a whole number from 0 to 20, and so is every number in the sums.
Is it safe for children?
Block Adder has no ads, no chat, no sign-up and no tracking. Nothing your child does is sent anywhere: the game in progress, the best scores and the statistics are kept only in this browser.
Does it work on a phone or tablet?
Yes. Tap a column to drop the block there. It fits a phone held upright, and it works with a mouse or the keyboard on a computer.
Keyboard
| 1 to 5 | Drop into that column |
|---|---|
| Left and right arrows | Move between columns |
| Enter or Space | Drop into the chosen column |
| H | Hint |