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 4.0 mi/h, the time to go one mile decreases by 11 s. What was your original speed?

Question

I used the equation V=d/t; I rearranged it to V=(1/t-11)-4. But then I end up with 2 variables. Any help?

1mile=v*t
1mile= (v+4)(t-11)
solve for t in the first equation
t= 1/v
Put that into the second equation
1= (v+4)(1/v -11)
multiply both sides by v
v= (v+4)(1-11v)
multiply out the RHS
rearragne the terms to be a quadratic, and solve.

Answer 1

41 m/h