Question 649316

1.	Two trains leave a city, traveling in opposite directions. One train is 20 mph faster than the second. After 5 hours the trains are 800 miles apart. What is the speed of each train? can u tell me the formula to solve this.. and how to do it without distance.. been trying for hours and I have a final tommorow!!


Let the speed of the slower train be S
Then the speed of the faster train = S + 20


Distance traveled by slower train, plus distance traveled by faster train = distance apart, OR


5S + 5(S + 20) = 800


5S + 5S + 100 = 800


10S = 800 - 100


10S = 700


S, or speed of slower train = {{{700/10}}}, or {{{highlight_green(70)}}} mph


Speed of faster train = 70 + 20, or {{{highlight_green(90)}}} mph


OR


Time * sum of speeds = distance apart


5(S + S + 20) = 800


{{{2S + 20 = 800/5}}}


2S + 20 = 160


2S = 140 ----- S = {{{140/2}}}, or 70 mph (slower)
70 + 20, or 90 mph (faster)


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