Your question:

A stadium is painted gold, blue and red in the ratio 5:4:2. It is estimated that the stadium has a paintable area of 445.5m2. If 1 litre of paint covers 15m2, find the amount required of each paint colour. (in whole litres)

Solution:

1) First we find out what is the area to be covered by each colour. The ratio of 
5:4:2 means that for every 5 parts of gold, you use 4 parts of blue and 2 parts
of red. So in a total of (11) parts, gold is 5, blue = 4 and red = 2.

2) So gold forms 5/11 of the area, blue covers 4/11 and red covers 2/11.

3) Since total area is 445.5,

Area covered by gold = 445.5*5/11 = 202.5 m^2
Area covered by blue = 445.5*4/11 = 162.0 m^2
Area covered by red  = 445.5*2/11 =  81.0 m^2

(Quick check: 202.5 + 162 + 81 should total up to 445.5, which it does)

4) Now since you need 1 liter of paint for 15 m^2 it is easy to find how many 
liters you need for each colour.

Liters of gold paint = 202.5/15 = 13.5 liters
Liters of blue paint = 162.0/15 = 10.8 liters
Liters of red paint  =  81.0/15 =  5.4 liters

:)