A number consisting of 2 identical digits, say xx
is multiplied by 99
Write down the product P, given its tens digit (i.e. 3rd from the left) is y.
(In reply to Solution (spoiler)
Building on Armando's solution
We get P =
1000*(9-y) + 100*(8-y) + 10y + y+1
= 9801 - 1089y