Five years ago, the average age of A, B, C and D was 45 yr. with E joining them now, the average of all the five is 49 yr. How old is E?

Ok its 45 because we have to add 5 years to the age of those four persons 5*4 exactly

49*5- 45*4= age of E =65
In the above solution why 4*5 is required because this is the simple calculation

Why (4*5) to perform ?

Avg_5yrs ago = A+B+C+D/4 = 45 (age of each person will be taken as 45)
When E joins avg becomes 49.
But as given in question person E joins 5 years later.
And the age of a person is not constant, i.e. it will change with time.
So 5 years later, the age of A, B, C, D will increase by 5 and become 50 years.

Thus, now avg of ABCD 5 yrs later will become 50.

We know that A+B+C+D+E/5 = 49, but we know the values of ABCD
hence, 50+50+50+50+E/5 = 49
E = 45 Years

65