Question

The average age of a committee of seven
trustees is the same as it was 5 years ago; a young man having been substituted for one of
them. The new man compared to the replaced old man, is younger in age by:
a. 5 years
b. 7 years
c. 12 years
d. 35 years​

Answer 1

Answer:

Lets assume that the sum of the age of the unchanged trustees 5 years ago be x. Also the age of the replaced trustee and the new trustee, five years ago be y and z respectively.

Now since the average age of the current committee and the previous committee is same,

(x + y)/7=(x + z + 35)/7

The 35 value accounts for the time lapse of 5 years for each of the 7 trustees.

Thus we get y - z = 35

Therefore the age gap is 35.