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Pebbles
Place four pebbles on the sand in the form of a square. Keep adding as few pebbles as necessary to double the area. How many extra pebbles are added each time?
It Figures
Suppose we allow ourselves to use three numbers less than 10 and multiply them together. How many different products can you find? How do you know you've got them all?
Bracelets
Investigate the different shaped bracelets you could make from 18 different spherical beads. How do they compare if you use 24 beads?
Age 7 to 14
Challenge Level
An introduction to Mathdokus, and ways in which they might be used in the classroom, can be found in the Teachers' Resources for the 3 by 3 Mathdokus.
For Primary teachers using this problem, you might also like your learners to work on Always, Sometimes or Never?, which appears in the same cell of the Primary curriculum mapping document.
You may also be interested in our other mathematical variations of Sudoku, which are suitable for Primary learners:
A First Product Sudoku
Intersection Sums Sudoku
Diagonal Sums Sudoku
For Secondary teachers using this problem, you might also like your students to work on Missing Multipliers, which appears in the same cell of the Secondary curriculum mapping document.
You may also be interested in our other mathematical variations of Sudoku:
Multiples Sudoku
Product Sudoku
LCM Sudoku
Difference Sudoku
This problem featured in the NRICH Primary and Secondary webinar in October 2022.
NRICH is part of the family of activities in the Millennium Mathematics Project.