rommysingh wrote:The number of antelope in a certain herd increases every year by a constant factor. If there are 500 antelope in the herd today, how many years will it take for the number of antelope to double?
(1) Ten years from now, there will be more than ten times the current number of antelope in the herd.
(2) If the herd were to grow in number at twice its current rate, there would be 980 antelope in the group in two years.
Question stem, rephrased:
At what rate does the herd increase each year?
Statement 1:
Here, the herd increases by MORE THAN A FACTOR OF 10 every ten years, but the EXACT rate of increase is unknown.
INSUFFICIENT.
Statement 2:
Here, TWICE the current rate over 2 years = (number of antelopes after 2 years)/(current number of antelopes) = (980)/(500) = 98/50 = 49/25.
Since (49/25) = (7/5)(7/5) -- at TWICE the current rate -- the herd is multiplied by a factor of 7/5 each year.
Since 7/5 = 140/100 = 140%, at TWICE the current rate the herd increases by 40% each year.
Thus, at the ACTUAL current rate, the herd increases by 20% each year.
SUFFICIENT.
The correct answer is
B.
Note:
We can conclude that statement 2 is sufficient without doing any actual math.
Since the value of twice the rate over 2 years is known, it must be possible to determine the actual rate of increase over 1 year.
SUFFICIENT.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at
[email protected].
Student Review #1
Student Review #2
Student Review #3
