First time: 30 miles from DC and second time 60 miles from DC

can someone give me a detailed explanation

Thanks

So imagine a line with point A--------------------B and will say the distance between them 120 miles. We will assume Ad=0 miles and Bd=120 miles.
imagine the 90 mph trains leave point B at t=0 and the 30 mile per hour train leaves point A at t=0

so at t=1 hour A is at the 30 mile marker and B is also at the 30 mile marker. (120 miles-90 mph(1hour))=30. so 30 is the first meeting point.

Now well assume they keep traveling for another hour

Now A is at the 60 mile marker (30 miles +30 mph(1hour))=60 miles
And B travels 90 miles in an hour, but after 30 miles it hits point A and has to turn back around and continue 60 more miles. So it is also at the 60 mile marker with A therefore 60 is the second meeting point

So 60 miles -30 miles=30 miles

I hope this helps

venmic wrote:can someone give me a detailed explanation

Thanks

in this questions .. first observe the speeds 30mph and 90mph means.. in one hour they both cover a distance of 120 miles(which is the distance bwtenn dc and balti) travelling in oppo directions.so DC trains(30mph) travels 30 miles in 1 hrs and in the same hr Baltimore trains covers remaining 90 miles ... so this is where they meet for the first time.which is 30 miles from DC and 90 miles from balti.