On his trip to Alaska, Joe traveled y percent of the total distance at an average speed of 50 miles per hour and the rest of the distance at an average speed of 70 miles per hour. What was Joe’s average speed in miles per hour for the whole trip in terms of y?
(A) 70(50 – y)
(B) (y + 60)/4
(C) 10,000 – 199y
(D) 17,500/(y + 250)
(E) y/2 + 35
If the first part is at 50 mile/h and the second part is 70 miles/h the overall speed is the toral distance / total time.
Pick a number for distance we can use 350. so the time for first part is 7 and for the rest is 5.
in the end we will have 26. something, but testing answer choices nothing comes up
(
where I'm wrong
PS: I could use a bit of logic and come to the answer easier, but .............
Say y=100%, so say Joe traveled entire trip at an average speed of 50 miles per hour. So, in this case we'd have that his average speed is simply 50 miles per hour.
Now, plug y=100 into the answer choices and see which one yields 50. Only answer choice D fits.
say y=0%. In this case we'd have that Joe's average speed is 70 miles per hour.
Now, plug y=0 into the answer choices and see which one yields 70. Again, only answer choice D fits.
Answer: D.