Two missiles head directly toward each other, one at 1200 mph, the other at 1800 mph. If they start 1763 miles apart, without using a pencil or calculator, how far will they be apart 1 minute before they collide?

1800mph + 1200mph = 3000mph (combined speed)
3000mph = 3000miles/60min = 50miles/min
Therefore, 1 min before they hit, they will be 50 miles apart (no matter where they start).