Thank you for another fantastic activity. This is what the students of yr 4 Maths Challenge Group at Lyneham ACT Australia came up with:
smallest numbers: 2-4-8-16, because doubling is the smallest you could do
biggest numbers: 5-25-50-100, how to define biggest? biggest number at the end and the sum = 180; 12-24-48-96 starts higher and has the same sum!
biggest difference between adjacent numbers: 5-10-20-100 after realising that 5-25-50-100 had a big gap between 100 and 50, but not the biggest
biggest range: 2-10-20-100, because it is even better than 5-10-20-100
Impossible numbers: working down from 99 doesn't work as you end up with 11 and can't go further; having 37 did not work either.
This highlighted they hadn't done prime numbers yet, so next on the program will be the Sieve of Eratosthenes!