Any help with this one? Those are the equations I have below, yet still cannot seem to figure this one out.
Jessica drove her car at a certain speed for the first 4 hours and increased its speed by 10 miles/hr, for the next two hours. If the total distance traveled by her was 500 miles, find the speeds at which Jessica drove her car at different times.
V1 = D1 / T1
V2 = V1 + 10
T1 = 4
Ttot = T1 + T2 = 6
Dtot= D1+D2 = 500
Vavg = Dtot / Ttot = 83 1/3
What I did was..
[(V1+V2) / 2 ] = Vavg
[((D1/4)+((D1/4)+10))) / 2 ] = Vavg
Solved for D1 then solved for V1 and got 78 1/3. Checked my math and is correct.
Is there any other way to solve this or did they just approximate in the answers?
These are possible answers:
80 and 90 miles/hr respectively
60 and 80 miles/hr respectively
50 and 60 miles/hr respectively