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Sequences, Series

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by sparkle6 » Mon Sep 26, 2011 8:49 am
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


[spoiler]Answer: B. Don't you need both statements?[/spoiler]
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Source: — Data Sufficiency |
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by cans » Mon Sep 26, 2011 9:11 am
Rn = Rn-1 + 3
A) first term=15. but with n, (no. of terms, median will vary)
insufficient
B) mean= 36
in arithmetic progression, mean=median
thus median=36
IMO B
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by sparkle6 » Mon Sep 26, 2011 10:55 pm
@Cans,

Can you expand on this statement if possible?

"in arithmetic progression, mean=median"
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by Anurag@Gurome » Tue Sep 27, 2011 2:52 am
sparkle6 wrote: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

[spoiler]Answer: B. Don't you need both statements?[/spoiler]
Rn = Rn-1 + 3 implies each term is 3 more than the previous term, like the series can be 3, 6, 9, 12,...
It means the given series is an arithmetic progression and for this type of series the mean of the set is always equal to the median.

(1) The first term of set R is 15 does not give any information using which we can find the value of mean, and hence the median of the set; NOT sufficient.

(2) The mean of set R is 36 implies the median of the set is also 36; SUFFICIENT.

The correct answer is B.
Anurag Mairal, Ph.D., MBA
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