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problem

Triangular clock

11 to 14

Trinni rearanges numbers on a clock face so each adjacent pair add up to a triangle number... What number did she put where 6 would usually be?

problem

In sum-mary

11 to 14

What does the sum of these three numbers tell us about their product?

problem

Sum of 1s

11 to 14

Can you find the last 5 digits of this sum?

problem

Favourite

Puzzling place value

14 to 16

Can you explain what is going on in these puzzling number tricks?

problem

Book codes

7 to 11

Look on the back of any modern book and you will find an ISBN code. Take this code and calculate this sum in the way shown. Can you see what the answers always have in common?

problem

Dodecawhat

14 to 16

Follow instructions to fold sheets of A4 paper into pentagons and assemble them to form a dodecahedron. Calculate the error in the angle of the not perfectly regular pentagons you make.