Number Cross uses a grid of numbers that at first glance might look a bit like a completed Sudoku puzzle. But contrary to Sudoku, Number Cross is a mathematical puzzle.
The goal is to cross out numbers inside the grid so that the remaining numbers in each row and column add up to the numbers outside it. Here's a a small example Number Cross puzzle:
Here’s what that puzzle looks like once it’s been solved:
Start with unique numbers. If a row or column total can only be made by a unique combination of numbers present in the grid, start there.
Look for the smallest and largest totals. Small totals mean more potential numbers that can be immediately crossed out. For example, if the total for a row is ‘2’, then anything larger than ‘2’ can be crossed out in that row. Similarly, very large totals usually require keeping the larger numbers in the grid, thus narrowing down your choices.
Track remaining options. In harder puzzles, for rows or columns where you're unsure of which numbers to cross out, it can help to make a list of possible combinations that add up to the required total. As other parts of the grid get filled in, some of these options will become invalid, leaving you with the answer.
As with all logic puzzles, practicing improves performance. The more puzzles you do, the better you well become at spotting common patterns and at recognising possible combinations.
Want to try your hand at Number Cross? We sometimes include them in our free Puzzle Weekly magazine – you should totally sign up for that if you haven’t already, as it puts 28 brand new puzzles in your inbox every week.
You can also find four levels of Number Cross in our Jumbo Adult Puzzle Book – which happens to include more than 500 puzzles of 20 different varieties.