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Digit Sum

What is the sum of all the digits in all the integers from one to one million?

Eight Dominoes

Using the 8 dominoes make a square where each of the columns and rows adds up to 8

Two and Two

How many solutions can you find to this sum? Each of the different letters stands for a different number.

Difference Sudoku

Age 14 to 16
Challenge Level

We received correct solutions from Cynthia and Lindsay from NLCSJeju, Jemma from Twynham School, and Lee from Lucton School.

Well done everyone! Here is Jemma's solution:

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.