SOLUTION: The 42km drive from Oakdale to Ridgemont usually takes 28 min. Because highway construction requires a reduced speed limit, the trip now takes 14 min longer. Find the reduced speed

Algebra ->  Customizable Word Problem Solvers  -> Evaluation -> SOLUTION: The 42km drive from Oakdale to Ridgemont usually takes 28 min. Because highway construction requires a reduced speed limit, the trip now takes 14 min longer. Find the reduced speed      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 118717: The 42km drive from Oakdale to Ridgemont usually takes 28 min. Because highway construction requires a reduced speed limit, the trip now takes 14 min longer. Find the reduced speed limit in km/h.
Found 2 solutions by m.hansen, MathLover1:
Answer by m.hansen(16) About Me  (Show Source):
You can put this solution on YOUR website!
distance = 42km
time = 28min + 14min = 42min
speed = distance%2Ftime
+speed+=+42km%2F42min+=+1+%28km%2Fmin%29 = 1 km/min
In more usual units of km/hr.
time+=+42min+%281+hr%2F60min%29= .7 hr
+speed+=+%2842km%2F.7hr%29+=+60+%28km%2Fhr%29+ = 60 km/hr

Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!
note that "v" is the variable for speed, that "d" is the variable for distance, and that "t" is the variable for time
the 42km drive from Oakdale to Ridgemont is your distance d
the time t+=+28+min
the speed is:
v+=+d%2Ft
Then usual speed is:
v+=+42km%2F28min….divide both sides by 14

v+=+3km%2F2min

v+=+%283%2F2%29%28km%2Fmin%29…………..since 1min is %281%2F60%29h, we will have

v+=+%28%283%2F2%29%2F%281%2F60%29%29%28km%2Fh%29…………..

v+=+%283%2A60%29km%2F%282h%29…………..simplify

v+=+%283%2A30%29km%2Fh…………..

v+=+90%28km%2Fh%29

let a reduced speed limit be v%5B1%5D

distance remain same

v%5B1%5D+=+d%2Ft%5B1%5D

since the trip now takes 14+min+longer, we can write the time as

t%5B1%5D+=+t+%2B+14min which is t%5B1%5D+=+28min+%2B+14min, or
t%5B1%5D=+42min
then

v%5B1%5D+=+42%2Akm%2F42%2Amin

v%5B1%5D+=+%2842%2F42%29%28km%2Fmin%29

v%5B1%5D+=+1%28km%2Fmin%29………. 1min is +%281%2F60%29%2Ah+, then we will have

v%5B1%5D+=+1km%2F%281%2F60%29h……….

v%5B1%5D+=+60%2A%28km%2Fh%29………. a reduced speed limit