Answer: After 1.7 hours, they will be 1,000 miles apart.
Step-by-step explanation:
Let t represent the time it will take both planes to be 1000 miles apart.
If both planes leave the airport at 10.00am, it means that they would have covered a total distance of 1000 miles after t hours.
Distance = speed × time
If the northbound plane flies at 280 mph, it means that the distance covered in t hours is 280t.
If the southbound plane flies at 320 mph, it means that the distance covered in t hours is 320t.
Since the total distance covered is 1000 miles, then
280t + 320t = 1000
600t = 1000
t = 1000/600
t = 1.7 hours
