Paul has 2/3 as many postcards as Shawn. The number of postcards Shawn has is 3/5 of the number of postcards Tim has. If the three boys have 280 postcards altogether, how many more postcards does Tim have than Paul?

P = (2 / 3) s;

s = (3 / 5) t;

p + s + t = 280;

Then, p = (2 / 3) (3 / 5) t;

p = (2 / 5) t;

We solve the equation : (2 / 5) t + (3 / 5) t + t = 280;

(2 / 5) t + (3 / 5) t + (5 / 5) t = (1400 / 5) t;

10t = 1400;

t = 1400 : 10;

t = 140 postcards has Tim;

p = (2 / 5) * 140 = 56 postcards has Paul;

s = (3 / 5) * 140 = 84 postcards has Shawn;