Question 112211

Distance(d)=Rate(r) times Time(t) or d=rt; t=d/r and r=d/t

Let t=number of hours that elapses after the second train leaves until the first train is overtaken

When the second train leaves, the first train has already 
travelled 72*3 or 216 mi

Now we know that when the two trains have travelled the same distance, the second train will have overtaken the first.

distance first train travels=216+72t
distance 2nd train travels=120t

So. our equation to solve is:

216+72t=120t  subtract 72t from both sides

216+72t-72t=120t-72t  collect like terms

216=48t  divide both sides by 48

t=4.5 hours-----------------------time it takes 2nd train to overtake the first train after the 2nd train leaves.

CK

216+72*4.5=120*4.5
540=540


Hope this helps---ptaylor