SOLUTION: A car is driven 280 miles. If it had gone 5 mph faster, it could have made the trip in 1 hr less time. what was the speed?

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Question 133407This question is from textbook
: A car is driven 280 miles. If it had gone 5 mph faster, it could have made the trip in 1 hr less time. what was the speed? This question is from textbook

Answer by vleith(2983) About Me  (Show Source):
You can put this solution on YOUR website!
Distance = speed * time
280+=+S+%2A+t+
+280%2FS+=+t+
If the car was drive 5 mph faster, it would have arrived 1 hour earlier. So
280+=+%28S%2B5%29+%2A+%28t-1%29
280+=+%28S%2B5%29+%2A+%28%28280%2FS%29+-1%29+
+280+=+%28S%2B5%29+%2A+%28%28280+-S%29%2FS%29+
+280+=+%28280+-+S%29+%2B+%285%28280+-S%29%29%2FS+
+0+=+-S+%2B+%281400+-5S%29%2FS+
+0+=+-S%5E2+-5S+%2B+1400+
+0+=+S%5E2+%2B+5S+-+1400+
+0+=+%28S+%2B+40%29+%28S++-+35%29+
S = -40 or S = 35. Since S can't be negative, S must be 35.
Check your answer.
280 / 35 = 8 hours
289 / 40 = 7 hours. Check!