Picking numbers(pick
smart numbers where computations will be easier when it comes to division/multiplication etc..) strategy.
I have tried to explain in detail but once u get the concept u can avoid all this extra verbage on the test (all of us will and get down to the actual calculations) and the calculations can be done quickly.
Let the distance = 240 (
picked 240 since its is a multiple of 60 and 40 and when I take x=50% then 120 will also be a multiple of 60 and 40 which makes calculations easier)
Let x = 50% i.e 50% of 240 = 120
remaining distance = 120
Time taken for first 120 = 120/40 =3
Time taken for next 120 = 120/60 = 2
Total time = 5
Tot distance = 240
Av speed = 240/5 = 48
When u substitute x=50 the answer choices should give u 48 as average speed
A (1800 - x) /2 -> (1800-50) /2 NO
B. (x + 60) /2 -> (50+60)/2 = 55 NO
C. (300 - x ) / 5 -> NO
D. 600 / (115 - x ) -> 600/115-50 = -> NO
E. 12,000 / ( x + 200)-> 12000/ (50+200) = 48 YES
Choose
E)
Always go with what you feel most comfortable with (algebric or picking numbers i.e one that can be solved within reasonable amount of time that u can allot to a question 2-2.5 mins max->3 on harder ones if needed)
and practice that skill the best u can before the exam.. The only downside(not really) when picking numbers for questions that have variables in the answer choices is that sometimes u may get 2 choices for which the numbers may work. You may have to pick new set of numbers to eliminate one of the 2 choices left. If we get stuck with algebric approach instead of wasting more time staring at the problem we must resort to picking numbers and solv these questions with variables in the answer choices. GMAC does not care how we solve a problem. Any approach conventional/textbook or unconventional works as long as we can get to to the correct answer within a reasonable time frame.
My bad for writing a textbook for this problem
but hope this helps!
Regards,
Cramya
