Lots of people sent in solutions for this one.
Becky from Wheelers Lane Junior School, Birmingham, England gave one of the best explanations ...
"I found this quite an easy puzzle because I know my times tables well. I soon spotted that 56, 28, 63 and 49 were all in the seven times table and later found out that 105 was. I also noticed that 100, 18, 65, 9 and 76 were not in the seven times table. I then worked out that 14 and 70 were".
As Susannah from Headington Junior School, Oxford says, "A ziffle is a multiple of 7".
Joshua from Ampthill, Bedfordshire, Emma from Cambridge and Matthew from Hethersett Old Hall Juniors also sent in correct solutions.