<span>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 mi let s = speed of the slower train then (s+4) = speed of the faster train : Write a time equation Slow train time - fast train time = 1 hr - = 1 multiply equation by s(s+4), cancel the denominators</span>360(s+4) - 360s = s(s+4)<span>360s + 1440 - 360s = s^2 + 4s A quadratic equation 0 = s^2 + 4s - 1440 Use the quadratic formula; a=1; b=4; c=-1440. but this will factor to: (s-36)(s+40) = 0 positive solution s = 36 mph, speed of the slow train then obviously; 40 mph, the speed of the faster : : Check this by finding the actual time of each 360/36 = 10 hrs 360/40 = 9 hrs, 1 hr less</span>
