Question 520806
Effective Speed = 540+720 = 1260 mph
Distance = 1890 miles

Time = Distance /  Speed
Time = 1890/1260
time = 1.5 hour.


After 1.5 hours two planes will be 1890 miles apart?



Check
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Plane A Data
============
Speed = 540 mph
Time = 1.5 hour
Distance covered = ?
Distance = Speed * Time
Distance covered= 540 * 1.5 = 810 miles


Plane B Data
============
Speed = 720 mph
Time = 1.5 hour
Distance covered = ?
Distance = Speed * Time
Distance covered = 720 * 1.5 = 1080 miles


Total Distance between two planes after 1.5 hours = 1080+810 = 1890 miles