Question

martha is 12 times older than her sister.she is 3 times younger than her brother.she is also 4 times older than her cousin .find the age of her cousin if their total age is 78

Answer 1

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Let cousin's age=x yrs
Then Martha's age=4x
Brother's age=4x/3
Sister's age=4x/12 
Now
x+4x+4x/3+4x/12=78
20x/3=78
x=78×(3/20)
x=11.7
Thus cousin's age =11.7 yrs

Answer 2

Question: Martha is 12 times older than her sister. She is 3 times younger than her brother. She is also 4 times older than her cousin. Find the age of her cousin, if their total age is 78.

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Solution:  Let Martha's age be $x$.

Then, her sister's age will be $\frac{x}{12}$.
          Her brother's age will be $3x$.
          Her cousins' age will be $\frac{x}{4}$. 

Values of $x$ :

Martha age =  $x$
Sister age = $\frac{x}{12}$
Brother age = $3x$
Cousin age = $\frac{x}{4}$

Condition or Clue: Their total age is 78.

So, the sum of $x$, $\frac{x}{12}$, $3x$, and $\frac{x}{4}$ is 78.

Equation:

$x+ \frac{x}{12}+3x+ \frac{x}{4}=78$

Solvation: 

$x+ \frac{x}{12}+3x+ \frac{x}{4}=78$

=>  $x+ \frac{x}{12}+ \frac{x}{4}+3x=78$

=>  $\frac{12x+x+4x+36x}{12}=78$

=>  $\frac{53x}{12}=78$

=>  $x= 78*\frac{12}{53}$

=>  $x= \frac{78*12}{53}$

=>  $x= \frac{936}{53}$

=>  $x=17.660377358490566037735849056604$

On rounding it up, we get -

$x=17.70$

Conclusion:

So, Martha's age is $x=17.70$.
Cousin's age is $\frac{x}{4}= 4.425$.