Two trains start heading toward each other from two cities, the distance between which is 720 km and meet right in the middle. the second train left 1 hour after the first train, but traveled at a speed 4 km/hour faster than the first train. find the speed of both trains.

If they met half-way, each train traveled 360 milet s = speed of the slower trainthen(s+4) = speed of the faster train: write a time equationslow train time - fast train time = 1 hr  -   = 1multiply equation by s(s+4), cancel the denominators
360(s+4) - 360s = s(s+4)360s + 1440 - 360s = s^2 + 4sa quadratic equation0 = s^2 + 4s - 1440use the quadratic formula; a=1; b=4; c=-1440. but this will factor to: (s-36)(s+40) = 0positive solutions = 36 mph, speed of the slow trainthen obviously; 40 mph, the speed of the faster  source: