Question 1072067: A 780-mile, 7-hour plane trip was flown at two speeds. For the first part of the trip, the average speed was 105 mph.
For the remainder of the trip, the average speed was 120 mph. How long did the plane fly at each speed?
105 mph
120 mph
Answer by ikleyn(52790)   (Show Source):
You can put this solution on YOUR website! .
A 780-mile, 7-hour plane trip was flown at two speeds. For the first part of the trip, the average speed was 105 mph.
For the remainder of the trip, the average speed was 120 mph. How long did the plane fly at each speed?
105 mph
120 mph
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Solution 1 (system of two equations)
x + y = 7, (1) (x is time flying at 105 mph; y is time flying at 120 mph)
105x + 120y = 780. (2)
Express x = 7-y from (1) and substitute into (2), then solve or y.
Solution 2 (one equation)
105*x _ 120*(7-x) = 780.
Solve for x.
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