MathDB

2014 preRMO p8, S, SU{15}, SU{15,1} have means M, M+2,M+1

Source:

August 9, 2019

Setsarithmetic mean

Problem Statement

Let

S

be a set of real numbers with mean

M

. If the means of the sets

S\cup \{15\}

and

S\cup \{15,1\}

are

M + 2

and

M + 1

, respectively, then how many elements does

S

have?