Quantitative Aptitude

Question

The average age of 7 members of a family is 18 years.

If the head of the family is excluded, the average age of the rest of the family would be 5 years less. Find the age of the head of the family.

Answer 1

Since the average age of all 7 members is 18, the sum of the ages of all 7 members is 7 * 18 = 126.

 

With the head of the family excluded, the average age is 5 less than 18, or 18 - 5 = 13.

 

The sum of the ages of the other six members is then 6 * 13 = 78.

 

The age of the head of the family is then the difference between the two sums:

 

Age of head of family = 126 - 78 = 48

Answer 2

assume total age of 7 members is X, then

X/7 = 18

total age of 7 members = 7 x 18 = 126 years

 

assume total age of 6 members is Y, then

Y/6 = (18-5)

total age of 6 members = 6 x 13 = 78 years

 

the age of the head of the family = X - Y = 126 - 78 = 48 years