8

Part of 2014 India PRMO

Problems(1)

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

Source:

S

be a set of real numbers with mean

M

. If the means of the sets

S\cup \{15\}

S\cup \{15,1\}

M + 2

M + 1

, respectively, then how many elements does

S

Setsarithmetic mean