Question 32426
Eastbound = x mph
Nothbound = x+20 mph
Westbound (if z)=> 2z = (x+20)+90; => z = (x+110)/2 mph;
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Eastbound in 7 hours = 7/x miles
North bound in 7 hours = 7/(x+20) miles
Westbound in 7 hours = 14/(x+110) miles
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East and West travel on the opposite direction
=> Distance between these two trains is the sum of the distances covered by them
=> 7/x + 14/(x+110) = 700
=> 1/x + 2/(x+110) = 100
=> 3x+110 = 100(x)(x+110)
=> 3x+110 = 100x^2 + 11000x
=> 100x^2 + 100097x - 110 = 0
..... The roots of the above equation will come in fracions; use quadratic formula to find the positive root.  Once x is found, you will be able to find the speed of all trains.