Answer:
Explanation:
Their total speed is (3800 mi)/(4 h) = 950 mi/h. This lets you write two equations for the speeds (x, y) of the two planes:
... x + y = 950
... x - y = 80 . . . . . . one travels 80 mi/h faster than the other
Adding the two equations gives
... 2x = 1030
... x = 515
... y = 515 -80 = 435
The speeds of the planes are 515 miles per hour and 435 miles per hour.
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Comment on the problem
This is a problem of the generic type "sum and difference problem." You are given the total of the two speeds and the difference between them. The higher speed is the average of those two numbers: (950+80)/2 = 515.
This is the generic solution for any "sum and difference problem:" the larger value is the average of the sum and difference.
