Question

A square wall, is covered with square tiles. There are 85 tiles altogether along the two diagonals. How many tiles are there on the whole wall?

Answer 1

Not counting the middle tile which both have we get 84.
 
Divide that by 2 because we have two diagonals.
 
We get 42 + 1 (middle tile) for one diagonal.

So one side has 43 tiles, too. The total number of tiles is 
$43^2=1849$