In Group A and B questions, students must complete the calculation on the opposite
side to where the is shown, and use this result to find the value of the missing number.
For example, in the first problem of Group B, students must first find 39 – 15; and having
found this to be 24, they then need to find the number which taken from 41 gives a result of
24 (or which added to 24 gives 41) for which the result is 17.