rommysingh wrote:Question 1
What is the median value of the set R, if for every term in the set, Rn = Rn-1 + 3?
(1) The first term of set R is 15.
(2) The mean of set R is 36.
Target question: What is the median value of the set R
Given: For every term in the set, Rn = Rn-1 + 3
In other words, if the first term is x, then the next term is x+3, and the next term is x+3+3, etc.
Statement 1: The first term of set R is 15
This statement doesn't
FEEL sufficient, so I'm going to TEST some values.
There are several sets that satisfy statement 1. Here are two:
Case a: R = {15, 18}, in which case
the median = 16.5
Case b: R = {15, 18, 21}, in which case
the median = 18
Since we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Aside: For more on this idea of plugging in values when a statement doesn't feel sufficient, you can read my article: https://www.gmatprepnow.com/articles/dat ... lug-values
Statement 2: The mean of set R is 36
We're already told that each number in the set is 3 greater than the number before it. This means the numbers in the set are EQUALLY SPACED.
There's a nice rule that says,
"In a set where the numbers are equally spaced, the mean will equal the median."
For example, in each of the following sets, the mean and median are equal:
{7, 9, 11, 13, 15}
{-1, 4, 9, 14}
{3, 4, 5, 6}
Since the numbers in set R are equally spaced, the mean must equal the median.
So,
the mean = median = 36
Since we can answer the
target question with certainty, statement 2 is SUFFICIENT
Answer =
B
Cheers,
Brent
