According to question ,
Total age of three youngsters = 33 × 3 – 11 × 3
Total age of three youngsters = 99 – 33 = 66 years

Correct Option: C

According to question ,
Total age of three youngsters = 33 × 3 – 11 × 3
Total age of three youngsters = 99 – 33 = 66 years
∴ Required average = 66 ÷ 3 = 22 years

Here , The average age of 7 children = 12
Total age of 7 children = 12 × 7
Age of died child = 6 years
Total age of remaining 6 children = 12 × 7 – 6 = 84 – 6
Total age of remaining 6 children = 78 years

Correct Option: A

Here , The average age of 7 children = 12
Total age of 7 children = 12 × 7
Age of died child = 6 years
Total age of remaining 6 children = 12 × 7 – 6 = 84 – 6
Total age of remaining 6 children = 78 years
∴ Their average age = 78 ÷ 6 = 13 years

Given that , 3 years ago, the average age of 5 members = 17 years.
Total present age of 5 members = 17 × 5 + 3 × 5
Born on new baby , the average age of 6 members = 17 years.
Total present age of 6 members = 17 × 6
Present age of child = 17 × 6 – (17 × 5 + 3 × 5)

Correct Option: C

Given that , 3 years ago, the average age of 5 members = 17 years.
Total present age of 5 members = 17 × 5 + 3 × 5
Born on new baby , the average age of 6 members = 17 years.
Total present age of 6 members = 17 × 6
Present age of child = 17 × 6 – (17 × 5 + 3 × 5)
Present age of child = 102 – (85 + 15)
∴ Present age of child = 102 – 100 = 2 years

Here , Five years ago, the average age of P and Q = 25.
Sum of the present age of P and Q = 2 × 25 + 10 = 60 years
The average age of P, Q and R today= 25 years
Sum of the present age of P, Q and R = 25 × 3 = 75 years

Correct Option: B

Here , Five years ago, the average age of P and Q = 25.
Sum of the present age of P and Q = 2 × 25 + 10 = 60 years
The average age of P, Q and R today= 25 years
Sum of the present age of P, Q and R = 25 × 3 = 75 years
∴ R’s present age = 75 – 60 = 15 years
∴ R’s age after 5 years = 15 + 5 = 20 years

The average age of 30 boys = 17 years
Age of replaced boy = 18 years
and another joining, the average age = 16.9 years
total decrease = 17 - 16.9 = 0.1 years
Age of new boy = 18 years – total decrease
Age of new boy = (18 – 0.1 × 30) years = 15 years
Second method to solve this question with the help of given formula :
Here, X = 17 – 16.9 = 0.1 , n = 30
Age of new boy = Age of replaced boy – Xn

Correct Option: D

The average age of 30 boys = 17 years
Age of replaced boy = 18 years
and another joining, the average age = 16.9 years
total decrease = 17 - 16.9 = 0.1 years
Age of new boy = 18 years – total decrease
Age of new boy = (18 – 0.1 × 30) years = 15 years
Second method to solve this question with the help of given formula :
Here, X = 17 – 16.9 = 0.1 , n = 30
Age of new boy = Age of replaced boy – Xn
Age of new boy = 18 – 0.1 × 30 = 18 – 3
∴ Age of new boy = 15 years