![6 by 6 Mathdokus](/sites/default/files/styles/medium/public/thumbnails/content-id-15108-icon.png?itok=K2WqWth-)
Mental calculations
![6 by 6 Mathdokus](/sites/default/files/styles/medium/public/thumbnails/content-id-15108-icon.png?itok=K2WqWth-)
![5 by 5 Mathdokus](/sites/default/files/styles/medium/public/thumbnails/content-id-15107-icon.png?itok=Shua5c9Y)
![4 by 4 Mathdokus](/sites/default/files/styles/medium/public/thumbnails/content-id-15106-icon.png?itok=6Zyctoxi)
![3 by 3 Mathdokus](/sites/default/files/styles/medium/public/thumbnails/content-id-15105-icon.png?itok=8AE1vli6)
![Mathdoku](/sites/default/files/styles/medium/public/thumbnails/content-id-2795-icon.png?itok=zx4sFH5r)
problem
Mathdoku
Complete the Mathdoku grid using the clues. Can you convince us that the number you have chosen for each square has to be correct?
![An Easy Way to Multiply by 10?](/sites/default/files/styles/medium/public/thumbnails/content-id-2772-icon.jpg?itok=jiT2oq21)
problem
An Easy Way to Multiply by 10?
Do you agree with Badger's statements? Is Badger's reasoning 'watertight'? Why or why not?
![Equivalent Pairs](/sites/default/files/styles/medium/public/thumbnails/content-id-14816-icon.jpg?itok=QnD2a1tJ)
![Arranging Additions and Sorting Subtractions](/sites/default/files/styles/medium/public/thumbnails/content-id-14726-icon.png?itok=JpyCE6wp)
problem
Arranging Additions and Sorting Subtractions
Order these four calculations from easiest to hardest. How did you decide?
![Subtraction Slip](/sites/default/files/styles/medium/public/thumbnails/content-id-14740-icon.jpg?itok=M2VCKxJ5)
problem
Subtraction Slip
Can you spot the mistake in this video? How would you work out the answer to this calculation?
![Compare the Calculations](/sites/default/files/styles/medium/public/thumbnails/content-id-14739-icon.png?itok=YPXkXLlg)
problem
Compare the Calculations
Can you put these four calculations into order of difficulty? How did you decide?