Solution:Average = (sum of elements)/(number of elements)
Given,
The average age of a father, a mother and a son 6 years ago was 30 years
Then, the average age of a father, a mother and a son at present = 30 + 6 = 36 years
At present, Total sum of ages of a father, a mother and a son = 36 × 3 = 108 years
The present average age of all four members of a family = 29 years
At present, Total sum of ages of all four members of a family
= 29 × 4 = 116 years
Daughter's present age = 116 − 108 = 8 years
Given,
At present,
The average age of a father and a mother is 46 years
Total sum of ages of a father and a mother
= 46 × 2 = 92 years
Total sum of ages of a son and a daughter
= 116 − 92 = 24
The present age of a son = 24 − 8 = 16 years
The difference between the present ages of a son and a daughter = 8 years
= 16 − 8
= 8 years
∴ The difference between the present ages of a son and a daughter is 8 years.