I'd like to share with you an alternative and very powerful technique for solving hard to grasp questions. These type of questions show up from time to time and this technique saved my ass when I was blocked, so it might help you out.
This technique is an ancient one I learned 11 years ago in my Physics class. I'll show you how to use it on a sample problem taken from OG12
, diagnostic test question 24 somehow edited:
Young padawan will jog from Yoda's training camp at x miles per hour and then walk back to the camp at y miles per hour. How many miles from the camp can padawan jog so that he spends a total of t hours jogging and walking?
E) (y+t)/x - t/y
If you don't know how to algebraically solve the problem, the trick is to analyze the units in the answer choices, let's see if they are homogeneous
x and y are speeds so their units are [distance / time]
A) yields a time, which is incorrect as we are looking for a distance.
B) is illegal, as we can't add a speed to a time.
C) yields a distance, so it could be the correct answer.
D) is illegal as we can't add speeds to a time
E) is illegal as we can't add a speed to a time.
Therefore answer C is correct.
Obviously if another answer looked like (xyt)/(x-y) then this trick wouldn't work as two (or more) answer choices would remain. But I noticed that for these questions, if you analyze the units, usually only one answer choice has the homogeneous units.
Keep me updated if this trick helped you out