John traveled 80% of the way from Yellow-town to Green-fields by train at an average speed of 80 miles per hour. The rest of the way John traveled by car at an average speed of v miles per hour. If the average speed for the entire trip was 60 miles per hour, what is v in miles per hour?
(a) 30
(b) 40
(c) 50
(d) 55
(e) 70
a – 30pmh
Correct answer is A.
Anyone with any good approach ???
Yeah it took me a min, but I got something..
Rate * Time = Distance
If you use 300 miles as your distance, and John travels 80 percent of that intially using the train, which would mean 240 miles, divided by his rate you get 3 hours of time. By knowing his final rate of 60 mph driving, and divde that by 300 you get a total time of 5 hours, so you subtract 5 hours from the 3 hours and you get 2 hours, and since the last bit of driving he does is 300-240=60 miles, and you divide by the 2 hour difference and you get 30.
(a) 30
Peter how do you guess 300 miles?
I took a traditional approach.
t1 + t2 = t
0.8D/80 + 0.2D/v = D/60
Solve for v.
distance /speed + distance /speed = speed/distance
let total distance be 100
80/80 + 20 / v = 100/60
v= 30
the answer should be A