This was a tricky problem. Well done to those of you who had a go. We had some very clearly explained answers.

The key was to work out the size of the booklet first. Sophie and Claire from The Downes School wrote:

1 x 1 didn't work because it said that two shortened rows have red discs.
2 x 2 didn't work because you need two shortened rows of red and one of orange.
3 x 3 didn't work because the total number of discs would be odd and you couldn't halve it. This means all odd numbers didn't work.
4 x 4 did work because you had the right amount of shortened rows.
6 x 6 didn't work because you can't divide 64 by 12.
8 x 8 didn't work because you need six whole rows.

Emma, Abi, Matthew B and Yuji from Moorfield Junior School; Keshinie and Sharon in Year 6 at Kilvington GGS Victoria, Australia; Gideon from Newberries Primary School and Hannah, Georgia, Patrick and Matthew from Brighton College Prep School realised that the number left after taking away the booklet must be a multiple of 12. Keshinie and Sharon describe how they continued from there:

So that made it 84.
Half of the disks are red so that made the amount of red 42.
Then it said that a quarter is black so that made it 21.
Then it said that one twelfth is blue so that made it 7.
Then it said that one complete row was filled with all of blue and green and the remainder of 10 if you take away 7 made it 3 green.
Then it said that one of the shortened rows is exactly filled with all the orange disks so that makes it 6.
Then it said that there was only one white disk.
Then we added all the numbers together making 80 disks so there was a remainder of 4 which had to be yellow.

We divided the 84 disks by the 6 orange ones that made it 14. So the fraction of orange had to be 1 out of 14 (1/14).
We divided the 84 disks by the 3 green disks making the answer 28. So the fraction of green had to be 1/28.
We already knew that the fraction of white disk was 1/84.
We divided the 84 disks by the 4 yellow ones making it 21 so the fraction of yellow had to be 1/21.