We found out that the solution was that there were 12 possible answers. These were:
7, 13, 14, 25, 26, 29, 31, 35, 47, 53, 58, 62.
We talked about how best to set this out, using a logical sequence.
Some children worked in ascending order, others worked in descending order.
For example:
Starting with 80's.
87 - 25 = 62 Then we did the same but with all the seventies as the
87 - 52 = 35 top number. We realised there would only be four options
85 - 72 = 13 for this as you can not take away eighties without being
85 - 27 = 58 in negative numbers. Similarly, with fifties at the top
82 - 75 = 7 there would only be two options because of negative
82 - 57 = 25 numbers. You can not put twenties at the top.
6 answers for eighties, 4 answers for seventies and 2 answers for fifties.
6 + 4 + 2 = 12 options.