Driving along a crowded freeway, you notice that it takes a time (t) to go from one mile marker to the next. When you increase your speed by 8.4 mi/hr, the time to go one mile decreases by 14 seconds. What was your original speed?

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For the first case: t1 = 1/v.. hr
For the second case (speed increase): t2 = 1/(v+8.4)... hr

The time difference is 14 sec = 14/3600 hr

t1-t2 = 14/3600 hr
1/v - 1/(v+8.4) = 14/3600 hr... Work with the left side fraction and then cross multiplication

8.4*3600 = 14 * v * (v + 8.4)
30240 = 14 * v * (v + 8.4)... Simplify again and use calculator to solve 2nd degree equation

V = 42.465 mi /hr

Good luck!