A friend of mine e-mailed this explanation
Quote:
It will always show the (selected sysmbol)
Any 2-digit number can be characterized as 10t+u, where t is the 10's digit,
resp. u the units.
The instructions are to compute 10t+u - (t+u)
Which is 9t + t + u - (t+u)
Which is 9t +t+u-t-u
Which is 9t
So your final number will certainly be one of 0, 9, 18, 27, ... 81
Peruse the chart: you will see that all of these have the (selected sysmbol) associated.
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