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Q.

The average age of a family of 5 members is 20 years. If the age of the youngest member be 10 years then what was the average age of the family at the time of the birth of the youngest member?

 A.

13.5

 B.

14

 C.

15

 D.

12.5

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Solution:
Option(D) is correct

At present the total age of the family = $5×20=100$

The total age of the family at the time of the birth of the youngest member:

$=\left[100−\underbrace{10}_\text{age of youngest}−\underbrace{(10×4)}_\text{10 years $\times$ remaining family members}\right]=50$

Therefore, average age of the family at the time of birth of the youngest member :

\(=\dfrac{50}{4}\)

\(=12.5\)


(6) Comment(s)


SRAVANTHI
 ()

SRAVANTHI its vary easy method once u practice its easy:

5*20=100 (hear 5 is all members & 20 is age)

1*10=10 ( hear 1 is youngest person & 10 is his age)

then 5-1=4 (subtraction) & 100-10=90 (subtraction)

then 90*1/4 = 22.5 hear 22.5 is avg age of a family (hear 1 is youngest member & 4 is remaining members of a family

now we want average age of the family at the time of the birth of the youngest member

so 22.5-10=12.5



Zoha Amjad
 ()

10 / 4 = 2.5

10 here is the age of the youngest person of the family, when he left his age will be divided into 4 to get an average.

20+2.5=22.5 is the average age of the family now

so now 10 years back the average age of the family will be 22.5-10=12.5



Anonymous
 ()

$10 \times 4 =$ the age of the youngest member multiplied by the rest of the family members (4)



Parul
 ()

$(10*4)$ is the term subtracting 10 years in the ages of the other members of the family.



Rahul Dixit
 ()

My question is same as above. I have failed to understand how you get $10*4.$



Akshata
 ()

How did you get $10*4$?

Couldn't understand this value