Q1- Distance, Time, and Speed An old car has to travel a 2-mile route, uphill and down. Because it is so old, the car can climb the first mile—the ascent—no faster than an average speed of 15 mi/h. How fast does the car have to travel the second mile—on the descent it can go faster, of course—to achieve an average speed of 30 mi/h for the trip?
what am i missing here?
why is the answer not 45 mi/h?
there is no time factor mentioned in the problem.
???
AS I said, with such questions you must get to what is actually being asked...careful attention to this will raise your score on any IQ test. This is one reason they are limited, because some people realize this and others do not.
What is asked here is, given two point separated by two miles, if it takes 4 minutes to go halfway can you cover the entire distance in exactly 4 minutes? Obviously not since even at light speed you cannot cover the remaining mile in 0.0 minutes. You could get very close but that is not good enough :-) i.e 29.99999...Avg Mph
The time factor is implicit in the phrase “average speed” i.e to have an average speed of 30mph you must cover two miles in exactly 4 minutes.
BTW, tho other question, the one that stumped Einsteins friend was this. (it seems rather simple to me)
2.Comparing Discounts Which price is better for the buyer, a 40% discount or two successive discounts of 20%?
Exactly what I was thinking.
Now... the exact number is unknown, due to the fact that the vehicle wouldn’t really have instantaneous acceleration.
The ‘time’ might help calculate the delta of the acceleration but that would only help on the uphill side.
Time is given in both cases, as speed is defined by ‘distance and time’ (mph).
Assuming ideological (and impossible) conditions...
1 mile at 15 mph +
1 mile at x mph = (15+x)/2
(15+x)/2=y
Given y=30
x=45
So.... what are we missing ?
You’ve got me scratching my head here and laughing. How can the car make it?
It is asking (ignoring all the irrelevant rubbish about hills and such) that you (or your car, or both of you) achieve an **average** velocity of 30 mph over the 2-mile distance.
To travel 2 miles at a velocity of 30 mph will require 4 minutes, whether uphill or down, or swimming through goo or whatever other nonsensical extraneous condition as to your mode of travel may be applicable. Velocity is velocity, ok?
If you travel the first mile at a velocity of only 15 mph, that first mile will -- guess what? -- require 4 minutes to traverse. Thus, to achieve an average velocity of 30 mph over the 2 mile trip, you will have precisely ZERO time left to travel the second mile and your velocity must therefore be "infinite" (which is an idiotic proposition on its face).
Contrary to your post, there is indeed a time factor mentioned in the problem, to wit, the problem's usage of VELOCITY, which is by definition DISTANCE PER UNIT OF TIME.
Got it now, mate?