Gujarati
Hindi
4.Average
hard

The average age of Donald, his wife and their two children is $23\, years.$ His wife is just $4 \,year$ younger than Donald himself andxhis wife was $24\, years$ old when his daughter was born. He was $32 \,years$ old when his son was born. Th average age of Donald and his daughter is ? (in $year$)

A

$25$

B

$22.5$

C

$26$

D

$23$

Solution

Let Donald be denoted by $H$ (Husband)

His wife be denoted by $W$, His daughter be denoted by $D$, His son be denoted by $S$

The average age of $4$ persons

$=\frac{H+W+D+S}{4}=23$

$H + W + D + S =92 \Rightarrow H = W +4$

  $H$   $W$ $D$ $S$
At the time when daughter is born $\rightarrow$ $28$ $\xleftarrow{{\left({+4}\right)}}$ $24$ $0$ $X$
  $\downarrow$        
At the time when Son is born$\rightarrow$ $32$ $\xleftarrow{{\left({-4}\right)}}$ $28$ $4$ $0$

So at the time of birth of his Son, total age of his family $=64$ $years.$ $(32+28+4+0=64)$ and presently the total age of his family $=92$ $years.$ It means total increase in age of the whole family $=28$ $years.$

Thus average increase in age $=\frac{28}{4}=7$ $years.$

It means the age of Donald $=39$ $years$ and age of his daughter $=11$ years Therefore the average age of Donald and his Daughter is $25\, years.$

Std 13
Quantitative Aptitude

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