GMAT Divisibility: List S...

List S consists of the positive integers that are multiples of 9 and are less than 100 . What is the median of the integers in S ?

divisibilitymediansequences & series

Explanation	Calculations	Help
$We first list the elements of S and determine how many terms there are.$	$S = {9, 18, ..., 99} n = \frac{99 - 9}{9} + 1 = \frac{90}{9} + 1 = 10 + 1 = 11$
$We note that S is an evenly spaced set so its median equals its average.$	$median = \frac{9 + 99}{2} = \frac{108}{2} = 54$

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54

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