Once you are confident that you can work systematically, why not try some of these challenges?
![Reach 100](/sites/default/files/styles/medium/public/thumbnails/content-02-09-penta2-icon.gif?itok=VCjD2daE)
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.
![Sticky Numbers](/sites/default/files/styles/medium/public/thumbnails/content-id-6571-icon.jpg?itok=gK-R2-2J)
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?
![ACE, TWO, THREE...](/sites/default/files/styles/medium/public/thumbnails/content-id-5775-icon.png?itok=fWWWcW02)
problem
ACE, TWO, THREE...
Can you picture how to order the cards to reproduce Charlie's card trick for yourself?
![Two and Two](/sites/default/files/styles/medium/public/thumbnails/content-01-06-six2-icon.png?itok=r2AsNoHS)
problem
Two and Two
How many solutions can you find to this sum? Each of the different letters stands for a different number.
![Product Sudoku](/sites/default/files/styles/medium/public/thumbnails/content-id-4903-icon.png?itok=VQGPrcYI)
problem
Product Sudoku
The clues for this Sudoku are the product of the numbers in adjacent squares.
![Pair Sums](/sites/default/files/styles/medium/public/thumbnails/content-97-01-six2-icon.jpg?itok=2AJBEkIH)
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?