I just got me a new cell phone and the first thing you wanna check is always the games section.
There was one free game available called city bloxx (sometimes called tower bloxx)
the aim is to build a city with a high population count.
There is an element of skill involved but let's eliminate it for the sake of argument.

The city is a 5 by 5 board where a building can be placed on one of the 25 squares.

you got 4 possible buildings:

Blue - houses 10 residents
Red - houses 20 residents
Green - houses 30 residents
Yellow - houses 40 residents

Blue can be placed anywhere, red must be at the building time placed adjacent (touching) a blue one. Green must touch a red and a blue, and Yellow must touch a blue, red and a green.

Buildings can be demolished and later replaced with a new building with a higher resident count given that the above rules are fulfilled.

A typical board looks something like this: http://en.wikipedia.org/wiki/Tower_Bloxx

What is the highest amount of residents a city can have on a 5x5 board.