Pocket Games
Sums
A grid of numbers, a target beside every row and column, and the job of deleting the ones you do not want. It looks like a game about addition and plays like the opposite: what matters is deciding what to take away.
The rules
The grid is full of numbers. Outside every row and every column there is a target. Your job is to delete some numbers so that the ones left in each row and each column add up to exactly the target beside it.
Every number belongs to a row and a column at the same time, and that is where the game comes from: deleting it to fix the row also changes the column’s total. The solution is unique, and you always get there by crossing between the two directions.
There are two tools: delete, for numbers that must go, and circle, for the ones you have decided to keep. Circling is not compulsory, but from the 5×5 up it is what holds your reasoning together: a circled number is a settled fact, and it shrinks the problem.
On Pocket Games
You play through levels, and the grid grows as you go:
| Levels | Grid | Numbers |
|---|---|---|
| 1–3 | 3×3 | 1 to 9 |
| 4–28 | 4×4 | 1 to 6 |
| 29–78 | 5×5 | 1 to 6 |
| 79–128 | 6×6 | 1 to 6 |
| 129–228 | 7×7 | 1 to 6 |
| 229 onwards | 6×6, 7×7 or 8×8 | 1 to 6 |
From the 4×4 up the numbers sit between 1 and 6 instead of 1 and 9: the closer together they are, the more combinations make the same total. From level 229 the game never ends, and the size depends only on the level number, so it is the same on every device; the numbers themselves are generated on the spot. A grid is only offered if a solver can close it by pure deduction, with a chain of steps that gets longer as the grid grows. Rows and columns that would have to be deleted or kept in full are thrown out too: a target of zero, or one equal to the whole row, never comes up here.
Below the grid there are three buttons, Erase, Keep and the hint: tapping a cell applies whichever is active.
- Three lives. A wrong move costs one, and the cell corrects itself. When they run out, in the app you can watch a video for one extra heart, once per level; in the browser the level restarts.
- One free hint per level, solving the cell you tap; after that, in the app, each hint costs a video, with no limit; in the browser there is only the free one.
- You do not have to decide every cell. The level closes as soon as you have erased every extra number or kept every right one: the rest fills itself in.
Only the level you reach is saved, and it syncs with your account: a level left halfway starts over.
How to deduce
The excess. Add up a row’s numbers and subtract the target: what remains is exactly how much you have to delete. If the excess is 4, you must delete numbers adding up to 4 — a 4, or a 3 and a 1. Often there is only one way to make that figure in that row, and the row closes itself.
The oversized number. If a row contains a number larger than its target, it goes without further thought: on its own it would already overshoot.
Crossing. This is the technique that solves the big grids. Once you have settled a cell via its row, look immediately at the column it belongs to: its excess has changed, and often there is now only one possible reading. Sums is played by constantly alternating directions, never by finishing one row at a time.
Common mistakes
- Finishing one row at a time. It does not work: the information comes from the crossings, and anyone working row by row gets stuck on the third.
- Not circling. Without the kept numbers, after ten moves you can no longer tell what you deduced from what you merely left alone.
- Trusting the excess without checking the columns. An excess that can be made two ways is not a deduction: it is a bet, and it costs a life.
Frequently asked questions
Do I have to mark the numbers I keep?
No. The level closes when you have erased every extra number, or when you have kept every right one: the other half fills itself in. Keeping numbers helps your reasoning, it does not score anything.
What happens if I run out of lives?
In the app, once per level, you can watch a video and carry on with one heart. Otherwise, and always in the browser, the level restarts with a new grid of the same size: the level you reached is not lost, and you do not go back to level one.
Can I leave a level halfway and come back to it?
No. Only the level reached is kept: if you leave halfway, you come back to the same level but with a new grid.
Does my level survive a change of phone?
Yes, if you sign in with your Google account: the level reached is synced, and across two devices the higher one wins.
Can it always be solved without guessing?
Yes. Grids are generated by requiring that a chain of deductions exists that closes them, and the minimum length of that chain grows with the size of the grid.
More games to try
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