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Adding All Nine
Make a set of numbers that use all the digits from 1 to 9, once and once only. Add them up. The result is divisible by 9. Add each of the digits in the new number. What is their sum? Now try some other possibilities for yourself!
Always the Same
Arrange the numbers 1 to 16 into a 4 by 4 array. Choose a number. Cross out the numbers on the same row and column. Repeat this process. Add up you four numbers. Why do they always add up to 34?
Age 11 to 14
Challenge Level
We have exactly $100$ coins. There are five different values of coins.
We have decided to buy a piece of computer software for $39.75$. We have the correct money, not a penny more, not a penny less!
Can you discover what the five different types of coins are worth and how many of each we have saved?
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NRICH is part of the family of activities in the Millennium Mathematics Project.
NRICH is part of the family of activities in the Millennium Mathematics Project.