Average age of 7 persons in a group is 30 years, the average age of five persons of this group is 31 years. What is the average age of the other two persons in this group?

 a) 55 years
 b) 15 years
 c) 26 years
 d) None of these

SSC CHSL-2015

None of these. Solution Total age of 5 person = (31 x 5) Let other two ages be p and q. Total average of 7 persons = [(31 x 5) + p + q]/7 = 30 p + q = 210 - 155 = 55 Average of other two persons = (p + q)/2 = 55/2 = 27.5