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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?


Investigate the different shaped bracelets you could make from 18 different spherical beads. How do they compare if you use 24 beads?

Surprising Split

Age 7 to 11 Challenge Level:

Here is another way of thinking about the trick...
For 54 x 11, set out a column addition with 54 as the first number to add.
Write 54 again, below the first 54, but this time line up the 4 in the ones column of the second 54 with the 5 in the tens column of the first 54.
Add them together:

column addition with 54 as the first number, then 54 written again below, but with the 5 in the hundreds column and the 4 in the tens column. The answer written is 594 

What digit is missing from the ones column of the second number in the sum?  
What do you know about numbers that end in that digit?
Why is this the same mathematically as the trick in the video?