Rates Question

[FilleNouvelle]

I feel like this is relatively simply, but for some reason I'm stumped.

There are 120 miles between cars A and B. They are travelling towards each other, car A at 40 mph and car B at 30 mph. How much space will be between them exactly one hour before they meet?

Answer is 70.

[e.cartman]

relative speed is 40+30 = 70mph which by definition says 70 "miles-per-hour"

[chestnut.cc]

maybe you could calculate when they would meet... let x be the distance from A and y be the distance from B when they meet... x+y=120... x = 40t... y = 30t... ie 70t = 120... ie t = 12/7... hence an hour before they meet ie t-1 = 5/7... x=200/7... y=150/7... 120- 350/7... ie 70...

[auyon]

Just think about it this way -- lets say they meet at some time T. Then "rewind" an hour, where will the trains be? One will be 30 miles away from that point and the other will be 40 miles away in the other direction. So an hour before they meet, they will be 30 + 40 miles = 70 miles apart.

[DattaPlot54321]

Thanks for the replies...though I feel awfully silly now, lol.