Your equation for the speed of the slower plane is

5x + 5(x+80) = 3650.

==========================================>

10x + 400 = 3650  ====>  10x = 3650 - 400 = 3250 ====>  x = 325 mph.


Answer. Slower plane speed 325 mph.  Faster plane speed 325+80 = 405 mph.

 

Answer by greenestamps(13206)   (Show Source): You can put this solution on YOUR website!
 
The distance of 3650 miles is covered by the two planes together in 5 hours, so the combined speeds of the two planes is 3650/5 = 730.


You can use formal algebra if you want to find the speed of each plane, knowing that their combined speed is 730 mph and that one plane's speed is 80 mph greater then the other's.


Or you can subtract the "extra" 80 mph of the faster plane to find that the two planes flying at the same speed would have a combined speed of 730-80=650 mph.  Then half of that for the slow plane is 325 mph, making the speed of the faster plane 325+80=405 mph. 

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