### Prime Magic

Place the numbers 1, 2, 3,..., 9 one on each square of a 3 by 3 grid so that all the rows and columns add up to a prime number. How many different solutions can you find?

### Domino Magic Rectangle

An ordinary set of dominoes can be laid out as a 7 by 4 magic rectangle in which all the spots in all the columns add to 24, while those in the rows add to 42. Try it! Now try the magic square...

### Fifteen

Can you spot the similarities between this game and other games you know? The aim is to choose 3 numbers that total 15.

# Difference Sudoku

##### Stage: 3 and 4 Challenge Level:
We received correct solutions from Cynthia and Lindsay from NLCSJeju, Jemma from Twynham School, Lee from Lucton School, and Scott (no school given). Well done everyone! Here is Jemma's solution:.pdf

Scott found a slightly different solution which you can see here:
.pdf
Jemma gave this explanation of how she solved the puzzle:

When I first looked at the difference Sudoku, I recognised that there were a few boxes where there was only one possible answer ( the ones with an eight difference); you just didn’t know which way round the numbers went. I found all of them, and experimented with them until I thought they were mostly right. I then worked on the bottom two lines as it gave you the most information for those two lines. I worked out the possible pairs and filled those two lines with the numbers 1-9 only once. Once I finished those two lines, I worked on the second and third rows to the top. Once I had filled them in, so it worked horizontally and vertically, I decided to try and finish the top row (to complete the top three boxes). That really helped me and allowed me to try and complete the rest of the difference Sudoku. Once I was finished, I looked back at my work and spotted one mistake; however, that could be easily fixed as all I had to do was switch two numbers round at the top, and switch two numbers round in the middle. I checked it, and didn’t find any more mistakes.