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**.

P&P only.

(In reply to

Solution (spoiler) by armando)

Building on Armando's solution

**P= (9-y,8-y,y,y+1)**

We get P =

1000*(9-y) + 100*(8-y) + 10y + y+1

= **9801 - 1089y**