<PRE><B>Question 133198</B>
ts=d, t=time, s=speed, d=distance
Let x be the speed of the freight train.
t=d/s In this problem the times are equal
So, d/s=d/s
322/x=392/(x+20)
322(x+20)=392x Multiply each side by x(x+20) to eliminate fractions.
322x+6440=392x
322x-322x+6440=392x-322x
6440=70x
70x/70=6440/70
x=92 mph
x+20=112 mph
.
Check:
322/92=3.5 hrs
392/112=3.5 hrs
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