Mock AIME 6 2006-2007 Problems/Problem 3

Alvin and Simon start $\frac{2+1}{2}(312)=468$ metres apart, as they are travelling in different directions. Simon and Theodore start $\frac{3-2}{3}(2526)=842$ metres apart, as they are travelling in the same direction. Therefore, Alvin and Simon are $842-468=\framebox{374}$ metres apart, as they are travelling in different directions. ~AbbyWong