Once you are confident that you can work systematically, why not try some of these challenges?
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problem
Reach 100
Choose four different digits from 1-9 and put one in each box so that the resulting four two-digit numbers add to a total of 100.
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problem
Sticky numbers
Can you arrange the numbers 1 to 17 in a row so that each adjacent pair adds up to a square number?
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problem
Ace, two, three...
Can you picture how to order the cards to reproduce Charlie's card trick for yourself?
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problem
Two and two
How many solutions can you find to this sum? Each of the different letters stands for a different number.
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problem
Product Sudoku
The clues for this Sudoku are the product of the numbers in adjacent squares.
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problem
Pair sums
Five numbers added together in pairs produce: 0, 2, 4, 4, 6, 8, 9, 11, 13, 15 What are the five numbers?