These always have clues that can be answered on their own. Solve these first, then look for clues that refer to them.

Use

on the menu to highlight clues that are ready to be answered. This saves time, but not brain power, so it’s not cheating!

If this method comes to halt, look for individual cells that can be filled rather than whole answers. For example; suppose you know that 1 Across ends in a 9, and you are given:

2 Down:1 across minus nine

4 Down:1 across times two

With a little thought, you’ll see that 2 Down must end in zero, and 4 Down ends in 8.

These are your friends. Once you know that something is even (say because it’s an even multiple of something else) or odd (such as a prime), then you can often deduce the odd or evenness of any related clues.

If you know something is odd or even, and another clue multiplies it by 5, you have the last digit.

These do not have simple entry points. You will always need to find clues that link to each other, or build the solution up from single cells.

Look for multiples of 5 or even numbers. Primes and squares often provide ways in.

If, for example, 4 times a two digit number also has two digits, that tells you something about both numbers. (In this case; the smaller one starts with 1 or 2, the larger is at least 40).

Whenever you have some knowledge about a possible answer, record it with the Notes facility (

or double-tap).You can select the possible digits for a given cell and enter notes about each clue. The pop-up also lists all the clues that refer to this one, which can save some searching.

The help pages are full of useful information about how to get the most out of X-Figure (tap ).

They include tables of squares, cubes, and primes.

Answers never start with a zero. If the clue is A Perfect Square, and there are two squares in the grid, the answer is not 09.

Turn on

to see how you’re getting on.If you’re really stuck on a Hard puzzle, use pencil mode to try out a train of thought.

- If you’re already using pencil, first select
- Then turn on
- Find a square with only a few possible digits, and pick one.
- Continue with the puzzle until you either encounter an impossibility or decide that the guess must have been correct.
- Finally, either or

X-Figure will show you the answer it has, highlighting cells where you have a different digit.

On rare occasions this may not be the only solution. If you complete the puzzle differently, but with all clues satisfied correctly, that’s fine - X-Figure will still recognise your version as correct.

All CodeWell apps are available under Apple’s Volume Purchase Program (VPP) which gives schools a 50% discount when buying 20 or more licenses. Many schools worldwide have taken advantage of this, installing the apps on school iPads or distributing copies to students.

CodeWell’s products are created by Alan Saul. For support or comments please email support1@codewell.co.uk or contact @iPhoneMaths on Twitter.

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