The average present age of four members of a family is 27 years and average increases by 3 years when one of their relatives joins them. The age of the relative is:

42 years

ATQ,

Sum of present age of family ⇒ 27×4 = 108

average age when relative joins = 30

sum of ages when relative joins ⇒ 30×5 = 150

∴ age of relative = 150-108 = 42