Question

The 2 age of 7 boys is increased by 1 year when one of tem whose age is replaced by a girl. What is the age of the girl ?
A) 33 yrs
B) 27 yrs
C) 21 yrs
D) 29 yrs

Answer 1

Let present age of P and Q be 3x3x and 4x4xrespectively.

Ten years ago, P was half of Q's age
⇒(3x−10)=12(4x−10)⇒6x−20=4x−10⇒2x=10⇒x=5⇒(3x−10)=12(4x−10)⇒6x−20=4x−10⇒2x=10⇒x=5

Total of their present ages

Answer 2

Q:

The average age of 7 boys is increased by 1 year when one of tem whose age is replaced by a girl. What is the age of the girl ?

A) 33 yrs
B) 27 yrs
C) 21 yrs
D) 29 yrs

Answer:   D) 29 yrs 

Read Description:

Let the avg age of 7 boys be 'p' years
Let the age of the girl be 'q' years

From given data,

The age of 7 boys = 7p years
Now the new average = (p + 1) when 22 yrs is replaced by q
Now the age of all 7 will become = 7(p + 1) yrs
Hence, 7p - 22 + q = 7(p + 1) yrs
7p - 22 + q = 7p + 7
q = 22 + 7 = 29

Therefore, the age of girl = q = 29 years.