Eve is painting the walls of a room.The walls have an area of 72m2 in total. To get the colour she wants, she mixes blue and red paint in the ratio 1:3.

Eve is painting the walls of a room.The walls have an area of 72m^2 in total. To get the colour she wants, she mixes blue and red paint in the ratio 1:3. 

Both colours of paint are sold in 1.5 liter tins. 

One litre of paint will cover an area of 9m^2.

Work out the minimum number of tins of each colour she has to buy 

Welll......she needs   72m^2/9m^2  = 8  litres

If the ratio is blue/:red =  1:3   she needs 3 times as much red as blue per mix

So........since she can't buy less than 1.5 litres of the blue.......then she must buy 1.5 litres of the blue.....which means that she must buy 1.5 x 3  = 4.5 litres of red.......however...this only gives her 6 total litres  [ 1.5 + 4.5]  and she needs 8

Thus......... she will have to buy another tin of blue  [ for a total of 3 litres of blue]  and 3 more tins of red = 4.5 litres

So.....she needs 2 tins of blue and 6 tins of red, for a total of [ 2 + 6 ]*1.5  = 12 litres

Finally.......she will have 4 extra litres of the mixture left  !!!!!