Question

$15$ men can build a wall $108$ m long in $6$ days, what is the length of similar wall that can be built by $25$ men in $3$ days?

• A. $75$
• B. $80$
• C. $85$
• D. $90$

Answer 1

Answer: (D)

$90$

As we are asked to find out the length of the wall we compare each item with the length as shown below:
More number of men$\Rightarrow$ More length of wall
Less number of men$\Rightarrow$ Less length of wall
i.e. This forms a direct relationship Moreover,
Less number of days$\Rightarrow$ Less length built
More number of days$\Rightarrow$ More length built
i.e. this relationship is also direct
Let x be the required length of the wall
Now we have two equations
Men $15:25$
Days$6:3::108:x$
Now to solve we multiply the given ratios together equaling the required ratio
i.e. $\frac{15}{25}\times \frac{6}{3}=\frac{108}{x}$
$\Rightarrow 15\times 6x=108\times 25\times 3$
$\Rightarrow x=\frac{108\times 25\times 3}{15\times 6}=18\times 5=90$